diff --git a/lib/clacks/activitypub.ex b/lib/clacks/activitypub.ex
index 9e7cd56..5c991d1 100644
--- a/lib/clacks/activitypub.ex
+++ b/lib/clacks/activitypub.ex
@@ -33,6 +33,7 @@ defmodule Clacks.ActivityPub do
           html :: String.t(),
           context :: String.t() | nil,
           in_reply_to :: String.t() | nil,
+          mentions :: [{String.t(), Clacks.Actor.t()}],
           id :: String.t() | nil,
           published :: DateTime.t(),
           to :: [String.t()],
@@ -43,6 +44,7 @@ defmodule Clacks.ActivityPub do
         html,
         context \\ nil,
         in_reply_to \\ nil,
+        mentions \\ [],
         id \\ nil,
         published \\ DateTime.utc_now(),
         to \\ [@public],
@@ -64,7 +66,15 @@ defmodule Clacks.ActivityPub do
       "conversation" => context,
       "context" => context,
       "inReplyTo" => in_reply_to,
-      "published" => published |> DateTime.to_iso8601()
+      "published" => published |> DateTime.to_iso8601(),
+      "tag" =>
+        Enum.map(mentions, fn {name, actor} ->
+          %{
+            "href" => actor.ap_id,
+            "name" => name,
+            "type" => "Mention"
+          }
+        end)
     }
   end
 
diff --git a/lib/clacks/user_actions_helper.ex b/lib/clacks/user_actions_helper.ex
index 5223824..3290307 100644
--- a/lib/clacks/user_actions_helper.ex
+++ b/lib/clacks/user_actions_helper.ex
@@ -1,26 +1,35 @@
 defmodule Clacks.UserActionsHelper do
-  alias Clacks.{User, Repo, Activity, Object, ActivityPub}
+  alias Clacks.{User, Repo, Activity, Object, ActivityPub, Actor}
 
   @public "https://www.w3.org/ns/activitystreams#Public"
 
   @spec post_status(
           author :: User.t(),
           content :: String.t(),
+          content_type :: String.t(),
           in_reply_to :: String.t() | Activity.t() | nil
         ) :: {:ok, Activity.t()} | {:error, any()}
 
-  def post_status(author, content, in_reply_to_ap_id) when is_binary(in_reply_to_ap_id) do
+  def post_status(_, _, content_type, _)
+      when not (content_type in ["text/plain", "text/markdown", "text/html"]) do
+    {:error, "invalid content type, must be text/plain, text/markdown, or text/html"}
+  end
+
+  def post_status(author, content, content_type, in_reply_to_ap_id)
+      when is_binary(in_reply_to_ap_id) do
     case Activity.get_by_ap_id(in_reply_to_ap_id) do
       nil ->
         {:error, "Could find post to reply to with AP ID '#{in_reply_to_ap_id}'"}
 
       in_reply_to ->
-        post_status(author, content, in_reply_to)
+        post_status(author, content, content_type, in_reply_to)
     end
   end
 
-  def post_status(author, content, in_reply_to) do
-    note = note_for_posting(author, content, in_reply_to)
+  def post_status(author, content, content_type, in_reply_to) do
+    {content, mentions} = convert_to_html(content, content_type)
+
+    note = note_for_posting(author, content, mentions, in_reply_to)
     note_changeset = Object.changeset_for_creating(note)
     {:ok, _object} = Repo.insert(note_changeset)
 
@@ -35,18 +44,48 @@ defmodule Clacks.UserActionsHelper do
     end
   end
 
-  defp note_for_posting(author, content, %Activity{
-         data: %{"id" => in_reply_to_ap_id, "context" => context, "actor" => in_reply_to_actor}
-       }) do
-    to = [in_reply_to_actor, @public]
+  @spec get_addressed(String.t(), [{String.t(), Actor.t()}], String.t() | nil) ::
+          {[String.t()], [String.t()]}
+  defp get_addressed(_author, mentions, in_reply_to_actor) do
+    to = [@public | Enum.map(mentions, fn {_, actor} -> actor.ap_id end)]
     # todo: followers
     cc = []
 
+    to =
+      case in_reply_to_actor do
+        nil -> to
+        in_reply_to_actor -> [in_reply_to_actor | to]
+      end
+
+    {
+      Enum.uniq(to),
+      Enum.uniq(cc)
+    }
+  end
+
+  @spec note_for_posting(User.t(), String.t(), [{String.t(), Actor.t()}], Activity.t() | nil) ::
+          map()
+
+  defp note_for_posting(author, content, mentions, in_reply_to) do
+    {context, in_reply_to_ap_id, in_reply_to_actor} =
+      case in_reply_to do
+        nil ->
+          {nil, nil, nil}
+
+        %Activity{
+          data: %{"id" => in_reply_to_ap_id, "context" => context, "actor" => in_reply_to_actor}
+        } ->
+          {context, in_reply_to_ap_id, in_reply_to_actor}
+      end
+
+    {to, cc} = get_addressed(author, mentions, in_reply_to_actor)
+
     ActivityPub.note(
       author.actor.ap_id,
       content,
       context,
       in_reply_to_ap_id,
+      mentions,
       nil,
       DateTime.utc_now(),
       to,
@@ -54,7 +93,76 @@ defmodule Clacks.UserActionsHelper do
     )
   end
 
-  defp note_for_posting(author, content, _in_reply_to) do
-    ActivityPub.note(author.actor.ap_id, content)
+  @spec convert_to_html(String.t(), String.t()) :: String.t()
+
+  defp convert_to_html(content, "text/html") do
+    content
+    |> replace_mentions()
+  end
+
+  defp convert_to_html(content, "text/markdown") do
+    content
+    |> Earmark.as_html!()
+    |> replace_mentions()
+  end
+
+  defp convert_to_html(content, "text/plain") do
+    {content, mentions} =
+      content
+      |> HtmlEntities.encode()
+      |> replace_links()
+      |> replace_mentions()
+
+    {String.replace(content, ["\r\n", "\n"], "<br>"), mentions}
+  end
+
+  @link_regex ~r/\bhttps?\S+\b/i
+
+  defp replace_links(content) do
+    Regex.replace(@link_regex, content, "<a href=\"\\1\">\\1</a>")
+  end
+
+  @mention_regex ~r/@(([a-z0-9_]+)(?:@[a-z0-9_\-.]+)?)/i
+
+  @spec replace_mentions(String.t()) :: {String.t(), [{String.t(), Actor.t()}]}
+
+  defp replace_mentions(content) do
+    Regex.scan(@mention_regex, content, return: :index)
+    |> Enum.reverse()
+    |> Enum.reduce({content, []}, fn [
+                                       {match_start, match_length},
+                                       {nickname_start, nickname_length},
+                                       {username_start, username_length}
+                                     ],
+                                     {content, mentions} ->
+      nickname = String.slice(content, nickname_start, nickname_length)
+
+      Actor.get_by_nickname(nickname)
+      |> case do
+        %Actor{} = actor ->
+          actor
+
+        nil ->
+          # todo: fetch by webfinger
+          raise "unimplemented"
+      end
+      |> case do
+        nil ->
+          {content, mentions}
+
+        actor ->
+          username = String.slice(content, username_start, username_length)
+
+          html =
+            "<span class=\"h-card\"><a href=\"#{actor.ap_id}\" class=\"u-url\">@#{username}</a></span>"
+
+          new_content =
+            String.slice(content, 0, match_start) <>
+              html <>
+              String.slice(content, (match_start + match_length)..String.length(content))
+
+          {new_content, [{nickname, actor} | mentions]}
+      end
+    end)
   end
 end
diff --git a/lib/clacks_web/controllers/frontend_controller.ex b/lib/clacks_web/controllers/frontend_controller.ex
index 0041a0b..6e2887c 100644
--- a/lib/clacks_web/controllers/frontend_controller.ex
+++ b/lib/clacks_web/controllers/frontend_controller.ex
@@ -254,7 +254,12 @@ defmodule ClacksWeb.FrontendController do
   def post_status(conn, %{"content" => content} = params) do
     current_user = conn.assigns[:user] |> Repo.preload(:actor)
 
-    UserActionsHelper.post_status(current_user, content, Map.get(params, "in_reply_to"))
+    UserActionsHelper.post_status(
+      current_user,
+      content,
+      "text/plain",
+      Map.get(params, "in_reply_to")
+    )
     |> case do
       {:ok, activity} ->
         path = Map.get(params, "continue", Routes.frontend_path(Endpoint, :status, activity.id))
diff --git a/lib/clacks_web/templates/frontend/_status.html.eex b/lib/clacks_web/templates/frontend/_status.html.eex
index f4e3cc7..f1284dc 100644
--- a/lib/clacks_web/templates/frontend/_status.html.eex
+++ b/lib/clacks_web/templates/frontend/_status.html.eex
@@ -16,7 +16,7 @@
     </p>
   </div>
   <div class="status-content e-content">
-    <%= @note["content"] %>
+    <%= raw(@note["content"]) %>
   </div>
   <div class="status-actions">
     <a href="<%= Routes.frontend_path(@conn, :reply, @status.id) %>">Reply</a>
diff --git a/mix.exs b/mix.exs
index 466e1e0..d3cde11 100644
--- a/mix.exs
+++ b/mix.exs
@@ -54,7 +54,9 @@ defmodule Clacks.MixProject do
       {:fast_sanitize, "~> 0.1.7"},
       {:fast_html, "~> 1.0.3"},
       {:dialyxir, "~> 1.0", only: [:dev], runtime: false},
-      {:floki, "~> 0.26.0"}
+      {:floki, "~> 0.26.0"},
+      {:earmark, "~> 1.4.4"},
+      {:html_entities, "~> 0.5.1"}
     ]
   end
 
diff --git a/mix.lock b/mix.lock
index b21e7f6..3e37fc5 100644
--- a/mix.lock
+++ b/mix.lock
@@ -11,6 +11,7 @@
   "db_connection": {:hex, :db_connection, "2.1.1", "a51e8a2ee54ef2ae6ec41a668c85787ed40cb8944928c191280fe34c15b76ae5", [:mix], [{:connection, "~> 1.0.2", [hex: :connection, repo: "hexpm", optional: false]}], "hexpm", "5a0e8c1c722dbcd31c0cbd1906b1d1074c863d335c295e4b994849b65a1fbe47"},
   "decimal": {:hex, :decimal, "1.8.0", "ca462e0d885f09a1c5a342dbd7c1dcf27ea63548c65a65e67334f4b61803822e", [:mix], [], "hexpm", "52694ef56e60108e5012f8af9673874c66ed58ac1c4fae9b5b7ded31786663f5"},
   "dialyxir": {:hex, :dialyxir, "1.0.0", "6a1fa629f7881a9f5aaf3a78f094b2a51a0357c843871b8bc98824e7342d00a5", [:mix], [{:erlex, ">= 0.2.6", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm", "aeb06588145fac14ca08d8061a142d52753dbc2cf7f0d00fc1013f53f8654654"},
+  "earmark": {:hex, :earmark, "1.4.4", "4821b8d05cda507189d51f2caeef370cf1e18ca5d7dfb7d31e9cafe6688106a4", [:mix], [], "hexpm", "1f93aba7340574847c0f609da787f0d79efcab51b044bb6e242cae5aca9d264d"},
   "ecto": {:hex, :ecto, "3.2.1", "a0f9af0fb50b19d3bb6237e512ac0ba56ea222c2bbea92e7c6c94897932c76ba", [:mix], [{:decimal, "~> 1.6", [hex: :decimal, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: true]}], "hexpm", "e1a1a1d72514b880d6bdd9fe9423d13a800ec1fb041c7239d885e5407b1fabce"},
   "ecto_sql": {:hex, :ecto_sql, "3.2.0", "751cea597e8deb616084894dd75cbabfdbe7255ff01e8c058ca13f0353a3921b", [:mix], [{:db_connection, "~> 2.1", [hex: :db_connection, repo: "hexpm", optional: false]}, {:ecto, "~> 3.2.0", [hex: :ecto, repo: "hexpm", optional: false]}, {:myxql, "~> 0.2.0", [hex: :myxql, repo: "hexpm", optional: true]}, {:postgrex, "~> 0.15.0", [hex: :postgrex, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "a2e23cf761668126252418cae07eff7967ad0152fbc5e2d0dc3de487a5ec774c"},
   "elixir_make": {:hex, :elixir_make, "0.6.0", "38349f3e29aff4864352084fc736fa7fa0f2995a819a737554f7ebd28b85aaab", [:mix], [], "hexpm", "d522695b93b7f0b4c0fcb2dfe73a6b905b1c301226a5a55cb42e5b14d509e050"},