diff --git a/src/activitypub/activity.rs b/src/activitypub/activity.rs
index fc97158..53e13c4 100644
--- a/src/activitypub/activity.rs
+++ b/src/activitypub/activity.rs
@@ -99,10 +99,11 @@ fn create_activity(
     activity
 }
 
-pub fn create_activity_note(
+pub fn create_note(
     config: &Config,
     post: &Post,
-) -> Activity {
+    in_reply_to: Option<&Post>,
+) -> Object {
     let object_id = get_object_url(
         &config.instance_url(),
         &post.id,
@@ -121,7 +122,18 @@ pub fn create_activity_note(
             url,
         }
     }).collect();
-    let object = Object {
+    let in_reply_to_object_id = match post.in_reply_to_id {
+        Some(in_reply_to_id) => {
+            let post = in_reply_to.unwrap();
+            assert_eq!(post.id, in_reply_to_id);
+            match post.author.actor_json {
+                Some(_) => None, // TODO: store object ID for remote posts
+                None => Some(get_object_url(&config.instance_url(), &post.id)),
+            }
+        },
+        None => None,
+    };
+    Object {
         context: Some(json!(AP_CONTEXT)),
         id: object_id,
         object_type: NOTE.to_string(),
@@ -130,10 +142,18 @@ pub fn create_activity_note(
         object: None,
         published: Some(post.created_at),
         attributed_to: Some(actor_id.clone()),
-        in_reply_to: None,
+        in_reply_to: in_reply_to_object_id,
         content: Some(post.content.clone()),
         to: Some(json!(AP_PUBLIC)),
-    };
+    }
+}
+
+pub fn create_activity_note(
+    config: &Config,
+    post: &Post,
+    in_reply_to: Option<&Post>,
+) -> Activity {
+    let object = create_note(config, post, in_reply_to);
     let activity = create_activity(
         &config.instance_url(),
         &post.author.username,
diff --git a/src/mastodon_api/statuses/views.rs b/src/mastodon_api/statuses/views.rs
index 8fc1aff..c49ff15 100644
--- a/src/mastodon_api/statuses/views.rs
+++ b/src/mastodon_api/statuses/views.rs
@@ -36,9 +36,15 @@ async fn create_status(
     let mut post_data = PostCreateData::from(data.into_inner());
     post_data.validate()?;
     let post = create_post(db_client, &current_user.id, post_data).await?;
-    let status = Status::from_post(post.clone(), &config.instance_url());
     // Federate
-    let activity = create_activity_note(&config, &post);
+    let in_reply_to = match post.in_reply_to_id {
+        Some(in_reply_to_id) => {
+            let in_reply_to = get_post_by_id(db_client, &in_reply_to_id).await?;
+            Some(in_reply_to)
+        },
+        None => None,
+    };
+    let activity = create_activity_note(&config, &post, in_reply_to.as_ref());
     let followers = get_followers(db_client, &current_user.id).await?;
     let mut recipients: Vec<Actor> = Vec::new();
     for follower in followers {
@@ -49,14 +55,16 @@ async fn create_status(
             recipients.push(actor);
         };
     };
+    let config_clone = config.clone();
     actix_rt::spawn(async move {
         deliver_activity(
-            &config,
+            &config_clone,
             &current_user,
             activity,
             recipients,
         ).await;
     });
+    let status = Status::from_post(post, &config.instance_url());
     Ok(HttpResponse::Created().json(status))
 }
 
diff --git a/src/models/posts/queries.rs b/src/models/posts/queries.rs
index ac8a37c..7f33c36 100644
--- a/src/models/posts/queries.rs
+++ b/src/models/posts/queries.rs
@@ -166,6 +166,8 @@ pub async fn get_post_by_id(
     Ok(post)
 }
 
+/// Given a post ID, finds all items in thread.
+/// Results are sorted by tree path.
 pub async fn get_thread(
     db_client: &impl GenericClient,
     post_id: &Uuid,