diff --git a/src/controllers/nostr/relay.ts b/src/controllers/nostr/relay.ts
index 8befa56..b304413 100644
--- a/src/controllers/nostr/relay.ts
+++ b/src/controllers/nostr/relay.ts
@@ -8,6 +8,7 @@ import {
   clientMsgSchema,
   type ClientREQ,
 } from '@/schemas/nostr.ts';
+import { Sub } from '@/subs.ts';
 
 import type { AppController } from '@/app.ts';
 import type { Event, Filter } from '@/deps.ts';
@@ -49,15 +50,24 @@ function connectStream(socket: WebSocket) {
   }
 
   /** Handle REQ. Start a subscription. */
-  async function handleReq([_, sub, ...filters]: ClientREQ) {
-    for (const event of await eventsDB.getFilters(prepareFilters(filters))) {
-      send(['EVENT', sub, event]);
+  async function handleReq([_, subId, ...filters]: ClientREQ): Promise<void> {
+    const prepared = prepareFilters(filters);
+
+    for (const event of await eventsDB.getFilters(prepared)) {
+      send(['EVENT', subId, event]);
     }
-    send(['EOSE', sub]);
+
+    send(['EOSE', subId]);
+
+    Sub.sub({
+      id: subId,
+      filters: prepared,
+      socket,
+    });
   }
 
   /** Handle EVENT. Store the event. */
-  async function handleEvent([_, event]: ClientEVENT) {
+  async function handleEvent([_, event]: ClientEVENT): Promise<void> {
     try {
       // This will store it (if eligible) and run other side-effects.
       await pipeline.handleEvent(event);
@@ -72,13 +82,12 @@ function connectStream(socket: WebSocket) {
   }
 
   /** Handle CLOSE. Close the subscription. */
-  function handleClose([_, _sub]: ClientCLOSE) {
-    // TODO: ???
-    return;
+  function handleClose([_, subId]: ClientCLOSE): void {
+    Sub.unsub({ id: subId, socket });
   }
 
   /** Send a message back to the client. */
-  function send(msg: RelayMsg) {
+  function send(msg: RelayMsg): void {
     return socket.send(JSON.stringify(msg));
   }
 }
diff --git a/src/filter.ts b/src/filter.ts
new file mode 100644
index 0000000..9cde0d1
--- /dev/null
+++ b/src/filter.ts
@@ -0,0 +1,27 @@
+import { type Event, matchFilters } from '@/deps.ts';
+
+import type { DittoFilter, EventData } from '@/types.ts';
+
+function matchDittoFilter(filter: DittoFilter, event: Event, data: EventData): boolean {
+  if (filter.local && !data.user) {
+    return false;
+  }
+
+  return matchFilters([filter], event);
+}
+
+/**
+ * Similar to nostr-tools `matchFilters`, but supports Ditto's custom keys.
+ * Database calls are needed to look up the extra data, so it's passed in as an argument.
+ */
+function matchDittoFilters(filters: DittoFilter[], event: Event, data: EventData): boolean {
+  for (const filter of filters) {
+    if (matchDittoFilter(filter, event, data)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+export { matchDittoFilters };
diff --git a/src/pipeline.ts b/src/pipeline.ts
index af72b79..a6eb15f 100644
--- a/src/pipeline.ts
+++ b/src/pipeline.ts
@@ -1,26 +1,49 @@
 import * as eventsDB from '@/db/events.ts';
 import { addRelays } from '@/db/relays.ts';
 import { findUser } from '@/db/users.ts';
-import { type Event } from '@/deps.ts';
+import { type Event, LRUCache } from '@/deps.ts';
 import { isLocallyFollowed } from '@/queries.ts';
+import { Sub } from '@/subs.ts';
 import { trends } from '@/trends.ts';
-import { isRelay, nostrDate } from '@/utils.ts';
+import { isRelay, nostrDate, nostrNow, Time } from '@/utils.ts';
+
+import type { EventData } from '@/types.ts';
 
 /**
  * Common pipeline function to process (and maybe store) events.
  * It is idempotent, so it can be called multiple times for the same event.
  */
 async function handleEvent(event: Event): Promise<void> {
+  if (encounterEvent(event)) return;
+  const data = await getEventData(event);
+
   await Promise.all([
-    storeEvent(event),
+    storeEvent(event, data),
     trackRelays(event),
     trackHashtags(event),
+    streamOut(event, data),
   ]);
 }
 
+/** Tracks encountered events to skip duplicates, improving idempotency and performance. */
+const encounters = new LRUCache<string, boolean>({ max: 1000 });
+
+/** Encounter the event, and return whether it has already been encountered. */
+function encounterEvent(event: Event) {
+  const result = encounters.get(event.id);
+  encounters.set(event.id, true);
+  return result;
+}
+
+/** Preload data that will be useful to several tasks. */
+async function getEventData({ pubkey }: Event): Promise<EventData> {
+  const user = await findUser({ pubkey });
+  return { user };
+}
+
 /** Maybe store the event, if eligible. */
-async function storeEvent(event: Event): Promise<void> {
-  if (await findUser({ pubkey: event.pubkey }) || await isLocallyFollowed(event.pubkey)) {
+async function storeEvent(event: Event, data: EventData): Promise<void> {
+  if (data.user || await isLocallyFollowed(event.pubkey)) {
     await eventsDB.insertEvent(event).catch(console.warn);
   } else {
     return Promise.reject(new RelayError('blocked', 'only registered users can post'));
@@ -63,6 +86,18 @@ function trackRelays(event: Event) {
   return addRelays([...relays]);
 }
 
+/** Determine if the event is being received in a timely manner. */
+const isFresh = ({ created_at }: Event): boolean => created_at >= nostrNow() - Time.seconds(10);
+
+/** Distribute the event through active subscriptions. */
+function streamOut(event: Event, data: EventData) {
+  if (!isFresh(event)) return;
+
+  for (const { socket, id } of Sub.matches(event, data)) {
+    socket.send(JSON.stringify(['EVENT', id, event]));
+  }
+}
+
 /** NIP-20 command line result. */
 class RelayError extends Error {
   constructor(prefix: 'duplicate' | 'pow' | 'blocked' | 'rate-limited' | 'invalid' | 'error', message: string) {
diff --git a/src/subs.ts b/src/subs.ts
new file mode 100644
index 0000000..82041c6
--- /dev/null
+++ b/src/subs.ts
@@ -0,0 +1,76 @@
+import { type Event } from '@/deps.ts';
+import { matchDittoFilters } from './filter.ts';
+
+import type { DittoFilter, EventData } from '@/types.ts';
+
+/** Nostr subscription to receive realtime events. */
+interface Subscription {
+  /** User-defined NIP-01 subscription ID. */
+  id: string;
+  /** Event filters for the subscription. */
+  filters: DittoFilter[];
+  /** WebSocket to deliver results to. */
+  socket: WebSocket;
+}
+
+/**
+ * Manages Ditto event subscriptions.
+ *
+ * Subscriptions can be added, removed, and matched against events.
+ *
+ * ```ts
+ * for (const sub of Sub.matches(event)) {
+ *   // Send event to sub.socket
+ *   sub.socket.send(JSON.stringify(event));
+ * }
+ * ```
+ */
+class SubscriptionStore {
+  #store = new Map<WebSocket, Map<string, Subscription>>();
+
+  /** Add a subscription to the store. */
+  sub(data: Subscription): void {
+    let subs = this.#store.get(data.socket);
+
+    if (!subs) {
+      subs = new Map();
+      this.#store.set(data.socket, subs);
+    }
+
+    subs.set(data.id, data);
+  }
+
+  /** Remove a subscription from the store. */
+  unsub(sub: Pick<Subscription, 'socket' | 'id'>): void {
+    this.#store.get(sub.socket)?.delete(sub.id);
+  }
+
+  /** Remove an entire socket. */
+  close(socket: WebSocket): void {
+    this.#store.delete(socket);
+  }
+
+  /**
+   * Loop through matching subscriptions to stream out.
+   *
+   * ```ts
+   * for (const sub of Sub.matches(event)) {
+   *   // Send event to sub.socket
+   *   sub.socket.send(JSON.stringify(event));
+   * }
+   * ```
+   */
+  *matches(event: Event, data: EventData): Iterable<Subscription> {
+    for (const subs of this.#store.values()) {
+      for (const sub of subs.values()) {
+        if (matchDittoFilters(sub.filters, event, data)) {
+          yield sub;
+        }
+      }
+    }
+  }
+}
+
+const Sub = new SubscriptionStore();
+
+export { Sub };
diff --git a/src/types.ts b/src/types.ts
index 096b847..beb184b 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -1,3 +1,4 @@
+import { UserRow } from '@/db.ts';
 import { type Filter } from '@/deps.ts';
 
 /** Custom filter interface that extends Nostr filters with extra options for Ditto. */
@@ -13,4 +14,8 @@ interface GetFiltersOpts {
   limit?: number;
 }
 
-export type { DittoFilter, GetFiltersOpts };
+interface EventData {
+  user: UserRow | undefined;
+}
+
+export type { DittoFilter, EventData, GetFiltersOpts };