diff --git a/modules/ruby/README.md b/modules/ruby/README.md
index 984b1a1..a95bc36 100644
--- a/modules/ruby/README.md
+++ b/modules/ruby/README.md
@@ -56,6 +56,24 @@ Aliases
   - `rbbp` packages gem files into *vendor/cache*.
   - `rbbu` updates gems to their latest version.
 
+Functions
+---------
+
+  - `ruby-info` exposes information about the Ruby environment via the
+    `$ruby_info` associative array.
+
+Theming
+-------
+
+To display the name of the current Ruby version in a prompt, define the
+following style in the `prompt_theme_setup` function.
+
+    # %v - ruby version.
+    zstyle ':prezto:module:ruby' version 'version:%v'
+
+Then add `$ruby_info[version]` to `$PROMPT` or `$RPROMPT` and call
+`ruby-info` in the `prompt_theme_preexec` hook function.
+
 Authors
 -------
 
diff --git a/modules/ruby/functions/ruby-info b/modules/ruby/functions/ruby-info
new file mode 100644
index 0000000..21dc1d6
--- /dev/null
+++ b/modules/ruby/functions/ruby-info
@@ -0,0 +1,28 @@
+#
+# Displays Ruby information.
+#
+# Authors:
+#   Sorin Ionescu <sorin.ionescu@gmail.com>
+#
+
+local version
+local version_format
+local version_formatted
+
+# Clean up previous $ruby_info.
+unset ruby_info
+typeset -gA ruby_info
+
+if (( $+commands[rvm-prompt] )); then
+  version="$(rvm-prompt)"
+elif (( $+commands[rbenv] )); then
+  version="$(rbenv version-name)"
+fi
+
+# Format version.
+if [[ -n "$version" ]]; then
+  zstyle -s ':prezto:module:ruby' version 'version_format'
+  zformat -f version_formatted "$version_format" "v:$version"
+  ruby_info[version]="$version_formatted"
+fi
+