diff --git a/NAMESPACE b/NAMESPACE
index cd0c1795e5a..976df8fc2a4 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -147,6 +147,7 @@ export(as_adjacency_matrix)
 export(as_biadjacency_matrix)
 export(as_bipartite)
 export(as_data_frame)
+export(as_directed)
 export(as_edgelist)
 export(as_graphnel)
 export(as_ids)
@@ -156,6 +157,7 @@ export(as_membership)
 export(as_phylo)
 export(as_star)
 export(as_tree)
+export(as_undirected)
 export(assortativity)
 export(assortativity.degree)
 export(assortativity.nominal)
diff --git a/R/conversion.R b/R/conversion.R
index 6d690240665..03c02dad121 100644
--- a/R/conversion.R
+++ b/R/conversion.R
@@ -412,11 +412,11 @@ as_edgelist <- function(graph, names = TRUE) {
 
 #' Convert between directed and undirected graphs
 #'
-#' `as.directed()` converts an undirected graph to directed,
-#' `as.undirected()` does the opposite, it converts a directed graph to
+#' `as_directed()` converts an undirected graph to directed,
+#' `as_undirected()` does the opposite, it converts a directed graph to
 #' undirected.
 #'
-#' Conversion algorithms for `as.directed()`: \describe{
+#' Conversion algorithms for `as_directed()`: \describe{
 #' \item{"arbitrary"}{The number of edges in the graph stays the same, an
 #' arbitrarily directed edge is created for each undirected edge, but the
 #' direction of the edge is deterministic (i.e. it always points the same
@@ -435,7 +435,7 @@ as_edgelist <- function(graph, names = TRUE) {
 #' graph contained loop edges.}
 #' }
 #'
-#' Conversion algorithms for `as.undirected()`: \describe{
+#' Conversion algorithms for `as_undirected()`: \describe{
 #' \item{"each"}{The number of edges remains constant, an undirected edge
 #' is created for each directed one, this version might create graphs with
 #' multiple edges.} \item{"collapse"}{One undirected edge will be created
@@ -445,11 +445,11 @@ as_edgelist <- function(graph, names = TRUE) {
 #' edges are ignored. This mode might create multiple edges if there are more
 #' than one mutual edge pairs between the same pair of vertices.  } }
 #'
-#' @aliases as.directed as.undirected
+#' @aliases as_directed as_undirected
 #' @param graph The graph to convert.
 #' @param mode Character constant, defines the conversion algorithm. For
-#'   `as.directed()` it can be `mutual` or `arbitrary`. For
-#'   `as.undirected()` it can be `each`, `collapse` or
+#'   `as_directed()` it can be `mutual` or `arbitrary`. For
+#'   `as_undirected()` it can be `each`, `collapse` or
 #'   `mutual`. See details below.
 #' @return A new graph object.
 #' @author Gabor Csardi \email{csardi.gabor@@gmail.com}
@@ -461,14 +461,14 @@ as_edgelist <- function(graph, names = TRUE) {
 #' @examples
 #'
 #' g <- make_ring(10)
-#' as.directed(g, "mutual")
+#' as_directed(g, "mutual")
 #' g2 <- make_star(10)
-#' as.undirected(g)
+#' as_undirected(g)
 #'
 #' # Combining edge attributes
 #' g3 <- make_ring(10, directed = TRUE, mutual = TRUE)
 #' E(g3)$weight <- seq_len(ecount(g3))
-#' ug3 <- as.undirected(g3)
+#' ug3 <- as_undirected(g3)
 #' print(ug3, e = TRUE)
 
 #' @examplesIf rlang::is_interactive()
@@ -485,23 +485,23 @@ as_edgelist <- function(graph, names = TRUE) {
 #'   9, 8, 9, 8, 9, 9, 10, 10, 10, 10
 #' ))
 #' E(g4)$weight <- seq_len(ecount(g4))
-#' ug4 <- as.undirected(g4,
+#' ug4 <- as_undirected(g4,
 #'   mode = "mutual",
 #'   edge.attr.comb = list(weight = length)
 #' )
 #' print(ug4, e = TRUE)
 #'
 #' @cdocs igraph_to_directed
-as.directed <- to_directed_impl
+as_directed <- to_directed_impl
 
-#' @rdname as.directed
+#' @rdname as_directed
 #' @param edge.attr.comb Specifies what to do with edge attributes, if
 #'   `mode="collapse"` or `mode="mutual"`.  In these cases many edges
 #'   might be mapped to a single one in the new graph, and their attributes are
 #'   combined. Please see [attribute.combination()] for details on
 #'   this.
 #' @export
-as.undirected <- function(graph, mode = c("collapse", "each", "mutual"), edge.attr.comb = igraph_opt("edge.attr.comb")) {
+as_undirected <- function(graph, mode = c("collapse", "each", "mutual"), edge.attr.comb = igraph_opt("edge.attr.comb")) {
   # Argument checks
   ensure_igraph(graph)
   mode <- switch(igraph.match.arg(mode),
@@ -1207,3 +1207,33 @@ as.matrix.igraph <- function(x, matrix.type = c("adjacency", "edgelist"), ...) {
     edgelist = as_edgelist(graph = x, ...)
   )
 }
+
+#' Convert between directed and undirected graphs
+#'
+#' @description
+#' `r lifecycle::badge("deprecated")`
+#'
+#' `as.directed()` was renamed to `as_directed()` to create a more
+#' consistent API.
+#' @inheritParams as_directed
+#' @keywords internal
+#' @export
+as.directed <- function(graph, mode = c("mutual", "arbitrary", "random", "acyclic")) {
+  lifecycle::deprecate_soft("2.0.4", "as.directed()", "as_directed()")
+  as_directed(graph, mode = mode)
+}
+
+#' Convert between undirected and unundirected graphs
+#'
+#' @description
+#' `r lifecycle::badge("deprecated")`
+#'
+#' `as.undirected()` was renamed to `as_undirected()` to create a more
+#' consistent API.
+#' @inheritParams as_undirected
+#' @keywords internal
+#' @export
+as.undirected <- function(graph, mode = c("collapse", "each", "mutual")) {
+  lifecycle::deprecate_soft("2.0.4", "as.undirected()", "as_undirected()")
+  as_undirected(graph = graph, mode = mode)
+}
diff --git a/R/flow.R b/R/flow.R
index 536b8a21056..607e70dc1ff 100644
--- a/R/flow.R
+++ b/R/flow.R
@@ -423,7 +423,7 @@ min_cut <- function(graph, source = NULL, target = NULL, capacity = NULL, value.
 #' vertex_disjoint_paths(g2, 100, 1)
 #'
 #' g <- sample_gnp(50, 5 / 50)
-#' g <- as.directed(g)
+#' g <- as_directed(g)
 #' g <- induced_subgraph(g, subcomponent(g, 1))
 #' cohesion(g)
 #'
@@ -527,7 +527,7 @@ vertex_connectivity <- function(graph, source = NULL, target = NULL, checks = TR
 #' edge_disjoint_paths(g2, 100, 1)
 #'
 #' g <- sample_gnp(50, 5 / 50)
-#' g <- as.directed(g)
+#' g <- as_directed(g)
 #' g <- induced_subgraph(g, subcomponent(g, 1))
 #' adhesion(g)
 #'
diff --git a/R/layout_drl.R b/R/layout_drl.R
index 2b66df1f20b..e9a600b02dc 100644
--- a/R/layout_drl.R
+++ b/R/layout_drl.R
@@ -92,7 +92,7 @@ layout.drl <- function(graph, use.seed = FALSE, seed = matrix(runif(vcount(graph
 #' @keywords graphs
 #' @examples
 #'
-#' g <- as.undirected(sample_pa(100, m = 1))
+#' g <- as_undirected(sample_pa(100, m = 1))
 #' l <- layout_with_drl(g, options = list(simmer.attraction = 0))
 #' plot(g, layout = l, vertex.size = 3, vertex.label = NA)
 #'
diff --git a/R/paths.R b/R/paths.R
index 50cdf2b88c9..f7c5e780d93 100644
--- a/R/paths.R
+++ b/R/paths.R
@@ -170,7 +170,7 @@ is_dag <- is_dag_impl
 #'
 #' g <- make_graph(c(1,2, 1,3, 2,4, 3,4), directed = TRUE)
 #' is_acyclic(g)
-#' is_acyclic(as.undirected(g))
+#' is_acyclic(as_undirected(g))
 #' @seealso [is_forest()] and [is_dag()] for functions specific to undirected
 #' and directed graphs.
 #' @family cycles
diff --git a/R/structural.properties.R b/R/structural.properties.R
index 4ded0c44b26..d765c2fc22f 100644
--- a/R/structural.properties.R
+++ b/R/structural.properties.R
@@ -1275,7 +1275,7 @@ subgraph.edges <- function(graph, eids, delete.vertices = TRUE) { # nocov start
 #'
 #' The `barrat` type of transitivity does not work for graphs with
 #' multiple and/or loop edges. If you want to calculate it for a directed
-#' graph, call [as.undirected()] with the `collapse` mode first.
+#' graph, call [as_undirected()] with the `collapse` mode first.
 #'
 #' @param graph The graph to analyze.
 #' @param type The type of the transitivity to calculate. Possible values:
diff --git a/man/as.directed.Rd b/man/as.directed.Rd
index 4a36a346c02..d1711005cc3 100644
--- a/man/as.directed.Rd
+++ b/man/as.directed.Rd
@@ -2,121 +2,22 @@
 % Please edit documentation in R/conversion.R
 \name{as.directed}
 \alias{as.directed}
-\alias{as.undirected}
 \title{Convert between directed and undirected graphs}
 \usage{
 as.directed(graph, mode = c("mutual", "arbitrary", "random", "acyclic"))
-
-as.undirected(
-  graph,
-  mode = c("collapse", "each", "mutual"),
-  edge.attr.comb = igraph_opt("edge.attr.comb")
-)
 }
 \arguments{
 \item{graph}{The graph to convert.}
 
 \item{mode}{Character constant, defines the conversion algorithm. For
-\code{as.directed()} it can be \code{mutual} or \code{arbitrary}. For
-\code{as.undirected()} it can be \code{each}, \code{collapse} or
+\code{as_directed()} it can be \code{mutual} or \code{arbitrary}. For
+\code{as_undirected()} it can be \code{each}, \code{collapse} or
 \code{mutual}. See details below.}
-
-\item{edge.attr.comb}{Specifies what to do with edge attributes, if
-\code{mode="collapse"} or \code{mode="mutual"}.  In these cases many edges
-might be mapped to a single one in the new graph, and their attributes are
-combined. Please see \code{\link[=attribute.combination]{attribute.combination()}} for details on
-this.}
-}
-\value{
-A new graph object.
 }
 \description{
-\code{as.directed()} converts an undirected graph to directed,
-\code{as.undirected()} does the opposite, it converts a directed graph to
-undirected.
-}
-\details{
-Conversion algorithms for \code{as.directed()}: \describe{
-\item{"arbitrary"}{The number of edges in the graph stays the same, an
-arbitrarily directed edge is created for each undirected edge, but the
-direction of the edge is deterministic (i.e. it always points the same
-way if you call the function multiple times).}
-\item{"mutual"}{Two directed edges are created for each undirected
-edge, one in each direction.}
-\item{"random"}{The number of edges in the graph stays the same, and
-a randomly directed edge is created for each undirected edge. You
-will get different results if you call the function multiple times
-with the same graph.}
-\item{"acyclic"}{The number of edges in the graph stays the same, and
-a directed edge is created for each undirected edge such that the
-resulting graph is guaranteed to be acyclic. This is achieved by ensuring
-that edges always point from a lower index vertex to a higher index.
-Note that the graph may include cycles of length 1 if the original
-graph contained loop edges.}
-}
-
-Conversion algorithms for \code{as.undirected()}: \describe{
-\item{"each"}{The number of edges remains constant, an undirected edge
-is created for each directed one, this version might create graphs with
-multiple edges.} \item{"collapse"}{One undirected edge will be created
-for each pair of vertices which are connected with at least one directed
-edge, no multiple edges will be created.} \item{"mutual"}{One
-undirected edge will be created for each pair of mutual edges. Non-mutual
-edges are ignored. This mode might create multiple edges if there are more
-than one mutual edge pairs between the same pair of vertices.  } }
-}
-\examples{
-
-g <- make_ring(10)
-as.directed(g, "mutual")
-g2 <- make_star(10)
-as.undirected(g)
-
-# Combining edge attributes
-g3 <- make_ring(10, directed = TRUE, mutual = TRUE)
-E(g3)$weight <- seq_len(ecount(g3))
-ug3 <- as.undirected(g3)
-print(ug3, e = TRUE)
-\dontshow{if (rlang::is_interactive()) (if (getRversion() >= "3.4") withAutoprint else force)(\{ # examplesIf}
-x11(width = 10, height = 5)
-layout(rbind(1:2))
-plot(g3, layout = layout_in_circle, edge.label = E(g3)$weight)
-plot(ug3, layout = layout_in_circle, edge.label = E(ug3)$weight)
-\dontshow{\}) # examplesIf}
-
-g4 <- make_graph(c(
-  1, 2, 3, 2, 3, 4, 3, 4, 5, 4, 5, 4,
-  6, 7, 7, 6, 7, 8, 7, 8, 8, 7, 8, 9, 8, 9,
-  9, 8, 9, 8, 9, 9, 10, 10, 10, 10
-))
-E(g4)$weight <- seq_len(ecount(g4))
-ug4 <- as.undirected(g4,
-  mode = "mutual",
-  edge.attr.comb = list(weight = length)
-)
-print(ug4, e = TRUE)
+\ifelse{html}{\href{https://lifecycle.r-lib.org/articles/stages.html#deprecated}{\figure{lifecycle-deprecated.svg}{options: alt='[Deprecated]'}}}{\strong{[Deprecated]}}
 
+\code{as.directed()} was renamed to \code{as_directed()} to create a more
+consistent API.
 }
-\seealso{
-\code{\link[=simplify]{simplify()}} for removing multiple and/or loop edges from
-a graph.
-
-Other conversion: 
-\code{\link{as.matrix.igraph}()},
-\code{\link{as_adj_list}()},
-\code{\link{as_adjacency_matrix}()},
-\code{\link{as_biadjacency_matrix}()},
-\code{\link{as_data_frame}()},
-\code{\link{as_edgelist}()},
-\code{\link{as_graphnel}()},
-\code{\link{as_long_data_frame}()},
-\code{\link{graph_from_adj_list}()},
-\code{\link{graph_from_graphnel}()}
-}
-\author{
-Gabor Csardi \email{csardi.gabor@gmail.com}
-}
-\concept{conversion}
-\keyword{graphs}
-\section{Related documentation in the C library}{\href{https://igraph.org/c/html/latest/igraph-Structural.html#igraph_to_directed}{\code{igraph_to_directed()}}.}
-
+\keyword{internal}
diff --git a/man/as.matrix.igraph.Rd b/man/as.matrix.igraph.Rd
index 7c55a76cc05..b74331c37e4 100644
--- a/man/as.matrix.igraph.Rd
+++ b/man/as.matrix.igraph.Rd
@@ -47,11 +47,11 @@ as.matrix(g, "adjacency", sparse = FALSE, attr = "weight")
 }
 \seealso{
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as_adj_list}()},
 \code{\link{as_adjacency_matrix}()},
 \code{\link{as_biadjacency_matrix}()},
 \code{\link{as_data_frame}()},
+\code{\link{as_directed}()},
 \code{\link{as_edgelist}()},
 \code{\link{as_graphnel}()},
 \code{\link{as_long_data_frame}()},
diff --git a/man/as.undirected.Rd b/man/as.undirected.Rd
new file mode 100644
index 00000000000..e97443382a7
--- /dev/null
+++ b/man/as.undirected.Rd
@@ -0,0 +1,23 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/conversion.R
+\name{as.undirected}
+\alias{as.undirected}
+\title{Convert between undirected and unundirected graphs}
+\usage{
+as.undirected(graph, mode = c("collapse", "each", "mutual"))
+}
+\arguments{
+\item{graph}{The graph to convert.}
+
+\item{mode}{Character constant, defines the conversion algorithm. For
+\code{as_directed()} it can be \code{mutual} or \code{arbitrary}. For
+\code{as_undirected()} it can be \code{each}, \code{collapse} or
+\code{mutual}. See details below.}
+}
+\description{
+\ifelse{html}{\href{https://lifecycle.r-lib.org/articles/stages.html#deprecated}{\figure{lifecycle-deprecated.svg}{options: alt='[Deprecated]'}}}{\strong{[Deprecated]}}
+
+\code{as.undirected()} was renamed to \code{as_undirected()} to create a more
+consistent API.
+}
+\keyword{internal}
diff --git a/man/as_adj_list.Rd b/man/as_adj_list.Rd
index d181b997f2e..b240ce1799f 100644
--- a/man/as_adj_list.Rd
+++ b/man/as_adj_list.Rd
@@ -66,11 +66,11 @@ as_adj_edge_list(g)
 \code{\link[=as_edgelist]{as_edgelist()}}, \code{\link[=as_adj]{as_adj()}}
 
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as.matrix.igraph}()},
 \code{\link{as_adjacency_matrix}()},
 \code{\link{as_biadjacency_matrix}()},
 \code{\link{as_data_frame}()},
+\code{\link{as_directed}()},
 \code{\link{as_edgelist}()},
 \code{\link{as_graphnel}()},
 \code{\link{as_long_data_frame}()},
diff --git a/man/as_adjacency_matrix.Rd b/man/as_adjacency_matrix.Rd
index 9ae327accef..db5a0c2343d 100644
--- a/man/as_adjacency_matrix.Rd
+++ b/man/as_adjacency_matrix.Rd
@@ -83,11 +83,11 @@ as_adjacency_matrix(g, attr = "weight")
 \code{\link[=graph_from_adjacency_matrix]{graph_from_adjacency_matrix()}}, \code{\link[=read_graph]{read_graph()}}
 
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as.matrix.igraph}()},
 \code{\link{as_adj_list}()},
 \code{\link{as_biadjacency_matrix}()},
 \code{\link{as_data_frame}()},
+\code{\link{as_directed}()},
 \code{\link{as_edgelist}()},
 \code{\link{as_graphnel}()},
 \code{\link{as_long_data_frame}()},
diff --git a/man/as_biadjacency_matrix.Rd b/man/as_biadjacency_matrix.Rd
index bc40afa0f65..c4cd1cd8ca3 100644
--- a/man/as_biadjacency_matrix.Rd
+++ b/man/as_biadjacency_matrix.Rd
@@ -62,11 +62,11 @@ as_biadjacency_matrix(g)
 \code{\link[=graph_from_biadjacency_matrix]{graph_from_biadjacency_matrix()}} for the opposite operation.
 
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as.matrix.igraph}()},
 \code{\link{as_adj_list}()},
 \code{\link{as_adjacency_matrix}()},
 \code{\link{as_data_frame}()},
+\code{\link{as_directed}()},
 \code{\link{as_edgelist}()},
 \code{\link{as_graphnel}()},
 \code{\link{as_long_data_frame}()},
diff --git a/man/as_directed.Rd b/man/as_directed.Rd
new file mode 100644
index 00000000000..73c9e213a56
--- /dev/null
+++ b/man/as_directed.Rd
@@ -0,0 +1,122 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/conversion.R
+\name{as_directed}
+\alias{as_directed}
+\alias{as_undirected}
+\title{Convert between directed and undirected graphs}
+\usage{
+as_directed(graph, mode = c("mutual", "arbitrary", "random", "acyclic"))
+
+as_undirected(
+  graph,
+  mode = c("collapse", "each", "mutual"),
+  edge.attr.comb = igraph_opt("edge.attr.comb")
+)
+}
+\arguments{
+\item{graph}{The graph to convert.}
+
+\item{mode}{Character constant, defines the conversion algorithm. For
+\code{as_directed()} it can be \code{mutual} or \code{arbitrary}. For
+\code{as_undirected()} it can be \code{each}, \code{collapse} or
+\code{mutual}. See details below.}
+
+\item{edge.attr.comb}{Specifies what to do with edge attributes, if
+\code{mode="collapse"} or \code{mode="mutual"}.  In these cases many edges
+might be mapped to a single one in the new graph, and their attributes are
+combined. Please see \code{\link[=attribute.combination]{attribute.combination()}} for details on
+this.}
+}
+\value{
+A new graph object.
+}
+\description{
+\code{as_directed()} converts an undirected graph to directed,
+\code{as_undirected()} does the opposite, it converts a directed graph to
+undirected.
+}
+\details{
+Conversion algorithms for \code{as_directed()}: \describe{
+\item{"arbitrary"}{The number of edges in the graph stays the same, an
+arbitrarily directed edge is created for each undirected edge, but the
+direction of the edge is deterministic (i.e. it always points the same
+way if you call the function multiple times).}
+\item{"mutual"}{Two directed edges are created for each undirected
+edge, one in each direction.}
+\item{"random"}{The number of edges in the graph stays the same, and
+a randomly directed edge is created for each undirected edge. You
+will get different results if you call the function multiple times
+with the same graph.}
+\item{"acyclic"}{The number of edges in the graph stays the same, and
+a directed edge is created for each undirected edge such that the
+resulting graph is guaranteed to be acyclic. This is achieved by ensuring
+that edges always point from a lower index vertex to a higher index.
+Note that the graph may include cycles of length 1 if the original
+graph contained loop edges.}
+}
+
+Conversion algorithms for \code{as_undirected()}: \describe{
+\item{"each"}{The number of edges remains constant, an undirected edge
+is created for each directed one, this version might create graphs with
+multiple edges.} \item{"collapse"}{One undirected edge will be created
+for each pair of vertices which are connected with at least one directed
+edge, no multiple edges will be created.} \item{"mutual"}{One
+undirected edge will be created for each pair of mutual edges. Non-mutual
+edges are ignored. This mode might create multiple edges if there are more
+than one mutual edge pairs between the same pair of vertices.  } }
+}
+\examples{
+
+g <- make_ring(10)
+as_directed(g, "mutual")
+g2 <- make_star(10)
+as_undirected(g)
+
+# Combining edge attributes
+g3 <- make_ring(10, directed = TRUE, mutual = TRUE)
+E(g3)$weight <- seq_len(ecount(g3))
+ug3 <- as_undirected(g3)
+print(ug3, e = TRUE)
+\dontshow{if (rlang::is_interactive()) (if (getRversion() >= "3.4") withAutoprint else force)(\{ # examplesIf}
+x11(width = 10, height = 5)
+layout(rbind(1:2))
+plot(g3, layout = layout_in_circle, edge.label = E(g3)$weight)
+plot(ug3, layout = layout_in_circle, edge.label = E(ug3)$weight)
+\dontshow{\}) # examplesIf}
+
+g4 <- make_graph(c(
+  1, 2, 3, 2, 3, 4, 3, 4, 5, 4, 5, 4,
+  6, 7, 7, 6, 7, 8, 7, 8, 8, 7, 8, 9, 8, 9,
+  9, 8, 9, 8, 9, 9, 10, 10, 10, 10
+))
+E(g4)$weight <- seq_len(ecount(g4))
+ug4 <- as_undirected(g4,
+  mode = "mutual",
+  edge.attr.comb = list(weight = length)
+)
+print(ug4, e = TRUE)
+
+}
+\seealso{
+\code{\link[=simplify]{simplify()}} for removing multiple and/or loop edges from
+a graph.
+
+Other conversion: 
+\code{\link{as.matrix.igraph}()},
+\code{\link{as_adj_list}()},
+\code{\link{as_adjacency_matrix}()},
+\code{\link{as_biadjacency_matrix}()},
+\code{\link{as_data_frame}()},
+\code{\link{as_edgelist}()},
+\code{\link{as_graphnel}()},
+\code{\link{as_long_data_frame}()},
+\code{\link{graph_from_adj_list}()},
+\code{\link{graph_from_graphnel}()}
+}
+\author{
+Gabor Csardi \email{csardi.gabor@gmail.com}
+}
+\concept{conversion}
+\keyword{graphs}
+\section{Related documentation in the C library}{\href{https://igraph.org/c/html/latest/igraph-Structural.html#igraph_to_directed}{\code{igraph_to_directed()}}.}
+
diff --git a/man/as_edgelist.Rd b/man/as_edgelist.Rd
index cb3db5ee491..9708cb79784 100644
--- a/man/as_edgelist.Rd
+++ b/man/as_edgelist.Rd
@@ -36,12 +36,12 @@ as_edgelist(g)
 \code{\link[=graph_from_adjacency_matrix]{graph_from_adjacency_matrix()}}, \code{\link[=read_graph]{read_graph()}}
 
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as.matrix.igraph}()},
 \code{\link{as_adj_list}()},
 \code{\link{as_adjacency_matrix}()},
 \code{\link{as_biadjacency_matrix}()},
 \code{\link{as_data_frame}()},
+\code{\link{as_directed}()},
 \code{\link{as_graphnel}()},
 \code{\link{as_long_data_frame}()},
 \code{\link{graph_from_adj_list}()},
diff --git a/man/as_graphnel.Rd b/man/as_graphnel.Rd
index 7f0b3f4377c..b4c33bac985 100644
--- a/man/as_graphnel.Rd
+++ b/man/as_graphnel.Rd
@@ -48,12 +48,12 @@ g4
 other graph representations.
 
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as.matrix.igraph}()},
 \code{\link{as_adj_list}()},
 \code{\link{as_adjacency_matrix}()},
 \code{\link{as_biadjacency_matrix}()},
 \code{\link{as_data_frame}()},
+\code{\link{as_directed}()},
 \code{\link{as_edgelist}()},
 \code{\link{as_long_data_frame}()},
 \code{\link{graph_from_adj_list}()},
diff --git a/man/as_long_data_frame.Rd b/man/as_long_data_frame.Rd
index 053e8077b5c..4e5e865dee9 100644
--- a/man/as_long_data_frame.Rd
+++ b/man/as_long_data_frame.Rd
@@ -32,12 +32,12 @@ as_long_data_frame(g)
 }
 \seealso{
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as.matrix.igraph}()},
 \code{\link{as_adj_list}()},
 \code{\link{as_adjacency_matrix}()},
 \code{\link{as_biadjacency_matrix}()},
 \code{\link{as_data_frame}()},
+\code{\link{as_directed}()},
 \code{\link{as_edgelist}()},
 \code{\link{as_graphnel}()},
 \code{\link{graph_from_adj_list}()},
diff --git a/man/edge_connectivity.Rd b/man/edge_connectivity.Rd
index 0530953375c..e2b96878aab 100644
--- a/man/edge_connectivity.Rd
+++ b/man/edge_connectivity.Rd
@@ -90,7 +90,7 @@ edge_connectivity(g2, 100, 1)
 edge_disjoint_paths(g2, 100, 1)
 
 g <- sample_gnp(50, 5 / 50)
-g <- as.directed(g)
+g <- as_directed(g)
 g <- induced_subgraph(g, subcomponent(g, 1))
 adhesion(g)
 
diff --git a/man/graph_from_adj_list.Rd b/man/graph_from_adj_list.Rd
index ec4022cf3c2..7a85ac68801 100644
--- a/man/graph_from_adj_list.Rd
+++ b/man/graph_from_adj_list.Rd
@@ -66,12 +66,12 @@ which_multiple(g3)
 \code{\link[=as_edgelist]{as_edgelist()}}
 
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as.matrix.igraph}()},
 \code{\link{as_adj_list}()},
 \code{\link{as_adjacency_matrix}()},
 \code{\link{as_biadjacency_matrix}()},
 \code{\link{as_data_frame}()},
+\code{\link{as_directed}()},
 \code{\link{as_edgelist}()},
 \code{\link{as_graphnel}()},
 \code{\link{as_long_data_frame}()},
diff --git a/man/graph_from_data_frame.Rd b/man/graph_from_data_frame.Rd
index afcbdd549a5..81465551cc5 100644
--- a/man/graph_from_data_frame.Rd
+++ b/man/graph_from_data_frame.Rd
@@ -129,11 +129,11 @@ for another way to create graphs, \code{\link[=read.table]{read.table()}} to rea
 from files.
 
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as.matrix.igraph}()},
 \code{\link{as_adj_list}()},
 \code{\link{as_adjacency_matrix}()},
 \code{\link{as_biadjacency_matrix}()},
+\code{\link{as_directed}()},
 \code{\link{as_edgelist}()},
 \code{\link{as_graphnel}()},
 \code{\link{as_long_data_frame}()},
diff --git a/man/graph_from_graphnel.Rd b/man/graph_from_graphnel.Rd
index c2b08071cd8..29469e22c36 100644
--- a/man/graph_from_graphnel.Rd
+++ b/man/graph_from_graphnel.Rd
@@ -62,12 +62,12 @@ g4
 graph representations.
 
 Other conversion: 
-\code{\link{as.directed}()},
 \code{\link{as.matrix.igraph}()},
 \code{\link{as_adj_list}()},
 \code{\link{as_adjacency_matrix}()},
 \code{\link{as_biadjacency_matrix}()},
 \code{\link{as_data_frame}()},
+\code{\link{as_directed}()},
 \code{\link{as_edgelist}()},
 \code{\link{as_graphnel}()},
 \code{\link{as_long_data_frame}()},
diff --git a/man/is_acyclic.Rd b/man/is_acyclic.Rd
index 13836664a8b..c00977d8c7e 100644
--- a/man/is_acyclic.Rd
+++ b/man/is_acyclic.Rd
@@ -23,7 +23,7 @@ cycles in undirected graphs.
 
 g <- make_graph(c(1,2, 1,3, 2,4, 3,4), directed = TRUE)
 is_acyclic(g)
-is_acyclic(as.undirected(g))
+is_acyclic(as_undirected(g))
 }
 \seealso{
 \code{\link[=is_forest]{is_forest()}} and \code{\link[=is_dag]{is_dag()}} for functions specific to undirected
diff --git a/man/layout_with_drl.Rd b/man/layout_with_drl.Rd
index 993d7066c2b..e77f6f62c95 100644
--- a/man/layout_with_drl.Rd
+++ b/man/layout_with_drl.Rd
@@ -97,7 +97,7 @@ There are five pre-defined parameter settings as well, these are called
 }
 \examples{
 
-g <- as.undirected(sample_pa(100, m = 1))
+g <- as_undirected(sample_pa(100, m = 1))
 l <- layout_with_drl(g, options = list(simmer.attraction = 0))
 plot(g, layout = l, vertex.size = 3, vertex.label = NA)
 
diff --git a/man/transitivity.Rd b/man/transitivity.Rd
index f0eebaead27..48bb8347a65 100644
--- a/man/transitivity.Rd
+++ b/man/transitivity.Rd
@@ -85,7 +85,7 @@ the edge weights are the same.
 
 The \code{barrat} type of transitivity does not work for graphs with
 multiple and/or loop edges. If you want to calculate it for a directed
-graph, call \code{\link[=as.undirected]{as.undirected()}} with the \code{collapse} mode first.
+graph, call \code{\link[=as_undirected]{as_undirected()}} with the \code{collapse} mode first.
 }
 \examples{
 
diff --git a/man/vertex_connectivity.Rd b/man/vertex_connectivity.Rd
index 6f421131305..1585b5a76f0 100644
--- a/man/vertex_connectivity.Rd
+++ b/man/vertex_connectivity.Rd
@@ -85,7 +85,7 @@ vertex_connectivity(g2, 100, 1)
 vertex_disjoint_paths(g2, 100, 1)
 
 g <- sample_gnp(50, 5 / 50)
-g <- as.directed(g)
+g <- as_directed(g)
 g <- induced_subgraph(g, subcomponent(g, 1))
 cohesion(g)
 
diff --git a/tests/testthat/_snaps/as.directed.md b/tests/testthat/_snaps/as.directed.md
new file mode 100644
index 00000000000..2e552572ea9
--- /dev/null
+++ b/tests/testthat/_snaps/as.directed.md
@@ -0,0 +1,22 @@
+# as.directed() deprecation
+
+    Code
+      is_directed(as.directed(g, mode = "mutual"))
+    Condition
+      Warning:
+      `as.directed()` was deprecated in igraph 2.0.4.
+      i Please use `as_directed()` instead.
+    Output
+      [1] TRUE
+
+# as.undirected() deprecation
+
+    Code
+      is_directed(as.undirected(g, mode = "collapse"))
+    Condition
+      Warning:
+      `as.undirected()` was deprecated in igraph 2.0.4.
+      i Please use `as_undirected()` instead.
+    Output
+      [1] FALSE
+
diff --git a/tests/testthat/test-alpha.centrality.R b/tests/testthat/test-alpha.centrality.R
index 9d18594246d..41274c96e13 100644
--- a/tests/testthat/test-alpha.centrality.R
+++ b/tests/testthat/test-alpha.centrality.R
@@ -64,7 +64,7 @@ test_that("undirected, alpha centrality works, #653", {
   ac2 <- alpha_centrality(g, sparse = FALSE)
   expect_equal(ac1, ac2)
 
-  g2 <- as.directed(g, mode = "mutual")
+  g2 <- as_directed(g, mode = "mutual")
   ac3 <- alpha_centrality(g, sparse = FALSE)
   expect_equal(ac1, ac3)
 })
diff --git a/tests/testthat/test-as.directed.R b/tests/testthat/test-as.directed.R
deleted file mode 100644
index 194e658d43c..00000000000
--- a/tests/testthat/test-as.directed.R
+++ /dev/null
@@ -1,36 +0,0 @@
-test_that("as.directed works", {
-  g <- sample_gnp(100, 2 / 100)
-  g2 <- as.directed(g, mode = "mutual")
-  g3 <- as.directed(g, mode = "arbitrary")
-  g4 <- as.directed(g, mode = "random")
-  g5 <- as.directed(g, mode = "acyclic")
-
-  expect_equal(degree(g), degree(g2) / 2)
-  expect_equal(degree(g), degree(g3))
-  expect_equal(degree(g), degree(g4))
-  expect_equal(degree(g), degree(g5))
-
-  expect_isomorphic(g, as.undirected(g2))
-  expect_isomorphic(g, as.undirected(g3))
-  expect_isomorphic(g, as.undirected(g4))
-  expect_isomorphic(g, as.undirected(g5))
-})
-
-test_that("as.directed keeps attributes", {
-  g <- graph_from_literal(A - B - C, D - A, E)
-  g$name <- "Small graph"
-  g2 <- as.directed(g, mode = "mutual")
-  g3 <- as.directed(g, mode = "arbitrary")
-  expect_equal(g2$name, g$name)
-  expect_equal(V(g2)$name, V(g)$name)
-  expect_equal(g3$name, g$name)
-  expect_equal(V(g3)$name, V(g)$name)
-
-  E(g)$weight <- seq_len(ecount(g))
-  g4 <- as.directed(g, "mutual")
-  df4 <- as_data_frame(g4)
-  g5 <- as.directed(g, "arbitrary")
-  df5 <- as_data_frame(g5)
-  expect_equal(df4[order(df4[, 1], df4[, 2]), ]$weight, c(1, 2, 1, 3, 3, 2))
-  expect_equal(df5[order(df5[, 1], df5[, 2]), ]$weight, 1:3)
-})
diff --git a/tests/testthat/test-as.undirected.R b/tests/testthat/test-as.undirected.R
deleted file mode 100644
index 9d4bf2fd5fd..00000000000
--- a/tests/testthat/test-as.undirected.R
+++ /dev/null
@@ -1,20 +0,0 @@
-test_that("as.undirected keeps attributes", {
-  g <- graph_from_literal(A + -+B, A - -+C, C + -+D)
-  g$name <- "Tiny graph"
-  E(g)$weight <- seq_len(ecount(g))
-
-  g2 <- as.undirected(g, mode = "collapse")
-  df2 <- as_data_frame(g2)
-  g3 <- as.undirected(g, mode = "each")
-  df3 <- as_data_frame(g3)
-  g4 <- as.undirected(g, mode = "mutual")
-  df4 <- as_data_frame(g4)
-
-  expect_equal(g2$name, g$name)
-  expect_equal(g3$name, g$name)
-  expect_equal(g4$name, g$name)
-
-  expect_equal(df2[order(df2[, 1], df2[, 2]), ]$weight, c(4, 2, 9))
-  expect_equal(df3[order(df3[, 1], df3[, 2]), ]$weight, c(1, 3, 2, 4, 5))
-  expect_equal(df4[order(df4[, 1], df4[, 2]), ]$weight, c(4, 9))
-})
diff --git a/tests/testthat/test-assortativity.R b/tests/testthat/test-assortativity.R
index 85a720a01a9..0cc0a56dce1 100644
--- a/tests/testthat/test-assortativity.R
+++ b/tests/testthat/test-assortativity.R
@@ -22,12 +22,12 @@ test_that("assortativity works", {
   expect_equal(assortativity_degree(g), assortativity_igraph)
   expect_equal(assortativity_degree(g), reference_assortativity(g))
 
-  asu <- assortativity_degree(simplify(as.undirected(g, mode = "collapse")))
+  asu <- assortativity_degree(simplify(as_undirected(g, mode = "collapse")))
   expect_equal(asu, -0.16319921031570466807)
 
   p <- read_graph(f <- gzfile("power.gml.gz"), format = "gml")
   expect_equal(assortativity_degree(p), assortativity(p, degree(p)))
-  expect_equal(assortativity_degree(p), reference_assortativity(as.directed(p, mode = "mutual")))
+  expect_equal(assortativity_degree(p), reference_assortativity(as_directed(p, mode = "mutual")))
 })
 
 test_that("nominal assortativity works", {
diff --git a/tests/testthat/test-attributes.R b/tests/testthat/test-attributes.R
index 118103a9e74..050d3f05718 100644
--- a/tests/testthat/test-attributes.R
+++ b/tests/testthat/test-attributes.R
@@ -185,8 +185,8 @@ test_that("cannot use vs/es from another graph", {
 test_that("attribute combinations handle errors correctly", {
   g <- make_graph(c(1, 2, 2, 1))
   E(g)$weight <- c("a", "b")
-  expect_error(as.undirected(g, edge.attr.comb = list(weight = "sum")), "invalid 'type'")
-  expect_error(as.undirected(g, edge.attr.comb = list(weight = sum)), "invalid 'type'")
+  expect_error(as_undirected(g, edge.attr.comb = list(weight = "sum")), "invalid 'type'")
+  expect_error(as_undirected(g, edge.attr.comb = list(weight = sum)), "invalid 'type'")
 })
 
 test_that("can change type of attributes (#466)", {
diff --git a/tests/testthat/test-centrality.R b/tests/testthat/test-centrality.R
index 121696c1861..efc0b74622d 100644
--- a/tests/testthat/test-centrality.R
+++ b/tests/testthat/test-centrality.R
@@ -19,6 +19,6 @@ test_that("subgraph_centrality() ignored edge directions", {
   g <- sample_gnm(10, 20, directed = TRUE)
   expect_equal(
     subgraph_centrality((g)),
-    subgraph_centrality(as.undirected(g, mode = "each"))
+    subgraph_centrality(as_undirected(g, mode = "each"))
   )
 })
diff --git a/tests/testthat/test-conversion.R b/tests/testthat/test-conversion.R
new file mode 100644
index 00000000000..27ec7370e56
--- /dev/null
+++ b/tests/testthat/test-conversion.R
@@ -0,0 +1,71 @@
+test_that("as_directed works", {
+  g <- sample_gnp(100, 2 / 100)
+  g2 <- as_directed(g, mode = "mutual")
+  g3 <- as_directed(g, mode = "arbitrary")
+  g4 <- as_directed(g, mode = "random")
+  g5 <- as_directed(g, mode = "acyclic")
+
+  expect_equal(degree(g), degree(g2) / 2)
+  expect_equal(degree(g), degree(g3))
+  expect_equal(degree(g), degree(g4))
+  expect_equal(degree(g), degree(g5))
+
+  expect_isomorphic(g, as_undirected(g2))
+  expect_isomorphic(g, as_undirected(g3))
+  expect_isomorphic(g, as_undirected(g4))
+  expect_isomorphic(g, as_undirected(g5))
+})
+
+test_that("as_directed keeps attributes", {
+  g <- graph_from_literal(A - B - C, D - A, E)
+  g$name <- "Small graph"
+  g2 <- as_directed(g, mode = "mutual")
+  g3 <- as_directed(g, mode = "arbitrary")
+  expect_equal(g2$name, g$name)
+  expect_equal(V(g2)$name, V(g)$name)
+  expect_equal(g3$name, g$name)
+  expect_equal(V(g3)$name, V(g)$name)
+
+  E(g)$weight <- seq_len(ecount(g))
+  g4 <- as_directed(g, "mutual")
+  df4 <- as_data_frame(g4)
+  g5 <- as_directed(g, "arbitrary")
+  df5 <- as_data_frame(g5)
+  expect_equal(df4[order(df4[, 1], df4[, 2]), ]$weight, c(1, 2, 1, 3, 3, 2))
+  expect_equal(df5[order(df5[, 1], df5[, 2]), ]$weight, 1:3)
+})
+
+test_that("as.directed() deprecation", {
+  local_igraph_options(print.id = FALSE)
+
+  g <- sample_gnp(100, 2 / 100)
+  expect_snapshot(is_directed(as.directed(g, mode = "mutual")))
+})
+
+test_that("as.undirected() deprecation", {
+  local_igraph_options(print.id = FALSE)
+
+  g <- sample_gnp(100, 2 / 100)
+  expect_snapshot(is_directed(as.undirected(g, mode = "collapse")))
+})
+
+test_that("as_undirected() keeps attributes", {
+  g <- graph_from_literal(A + -+B, A - -+C, C + -+D)
+  g$name <- "Tiny graph"
+  E(g)$weight <- seq_len(ecount(g))
+
+  g2 <- as_undirected(g, mode = "collapse")
+  df2 <- as_data_frame(g2)
+  g3 <- as_undirected(g, mode = "each")
+  df3 <- as_data_frame(g3)
+  g4 <- as_undirected(g, mode = "mutual")
+  df4 <- as_data_frame(g4)
+
+  expect_equal(g2$name, g$name)
+  expect_equal(g3$name, g$name)
+  expect_equal(g4$name, g$name)
+
+  expect_equal(df2[order(df2[, 1], df2[, 2]), ]$weight, c(4, 2, 9))
+  expect_equal(df3[order(df3[, 1], df3[, 2]), ]$weight, c(1, 3, 2, 4, 5))
+  expect_equal(df4[order(df4[, 1], df4[, 2]), ]$weight, c(4, 9))
+})
diff --git a/tests/testthat/test-dyad.census.R b/tests/testthat/test-dyad.census.R
index 7470f2206dc..828a50764f4 100644
--- a/tests/testthat/test-dyad.census.R
+++ b/tests/testthat/test-dyad.census.R
@@ -21,7 +21,7 @@ test_that("dyad_census works with celegansneural", {
   expect_equal(dc, list(mut = 197, asym = 1951, null = 41808))
   expect_equal(sum(which_mutual(ce)), dc$mut * 2)
   expect_equal(
-    ecount(as.undirected(ce, mode = "collapse")) - dc$mut,
+    ecount(as_undirected(ce, mode = "collapse")) - dc$mut,
     dc$asym
   )
   expect_equal(sum(unlist(dc)), vcount(ce) * (vcount(ce) - 1) / 2)
diff --git a/tests/testthat/test-trees.R b/tests/testthat/test-trees.R
index 9739b2f27cc..0d428c8707e 100644
--- a/tests/testthat/test-trees.R
+++ b/tests/testthat/test-trees.R
@@ -78,13 +78,13 @@ test_that("to_prufer and make_from_prufer works for trees", {
   g <- make_tree(13, 3, mode = "out")
   seq <- to_prufer(g)
   g2 <- make_from_prufer(seq)
-  g3 <- as.undirected(g)
+  g3 <- as_undirected(g)
   expect_true(isomorphic(g2, g3))
 
   g <- make_tree(13, 3, mode = "in")
   seq <- to_prufer(g)
   g2 <- make_from_prufer(seq)
-  g3 <- as.undirected(g)
+  g3 <- as_undirected(g)
   expect_true(isomorphic(g2, g3))
 })