diff --git a/src/event_system.c b/src/event_system.c
index 2d4f894..38513e9 100644
--- a/src/event_system.c
+++ b/src/event_system.c
@@ -110,14 +110,16 @@ RETURN_SYSTEM:
   return es;
 }
 
-void es_deinit(EventSystem event_system) {
-  if (IS_INVALID_SYSTEM(event_system)) {
+void es_deinit(EventSystem *event_system) {
+  if (!event_system || IS_INVALID_SYSTEM((*event_system))) {
     return;
   }
 
-  ESInternal *es = get_event_system_internal(event_system);
+  ESInternal *es = get_event_system_internal(*event_system);
 
   munmap(system, es->alloc_size);
+
+  event_system->id = 0;
 }
 
 Event es_register_event(EventSystem event_system) {
@@ -174,11 +176,88 @@ void es_deregister_event(EventSystem event_system, Event event) {
   }
 }
 
-EventListener es_add_event_listener(EventSystem event_system, Event event, EventCallback *listener) {}
+EventListener es_add_event_listener(EventSystem event_system, Event event, EventCallback callback) {
+  EventListener listener = INVALID_LISTENER;
 
-void es_remove_event_listener(EventSystem event_system, EventListener listener) {}
+  if (IS_INVALID_SYSTEM(event_system) || IS_INVALID_EVENT(event) || !callback) {
+    goto RETURN_LISTENER;
+  }
 
-void es_emit_event(EventSystem event_system, Event event, void *data) {}
+  ESInternal *es    = get_event_system_internal(event_system);
+  EventInternal *ev = get_event(es, event);
+
+  if (ev->free_count > 0) {
+    u64 id = ev->free[--(ev->free_count)];
+
+    ev->free[ev->free_count] = 0;
+    ev->callbacks[id]        = callback;
+
+    listener.id    = id;
+    listener.event = event;
+
+    goto RETURN_LISTENER;
+  }
+
+  if (ev->count >= ev->capacity) {
+    // TODO (Abdelrahman): Handle reallocating when out of callbacks
+    goto RETURN_LISTENER;
+  }
+
+  u64 id = ++(ev->count);
+
+  ev->callbacks[id] = callback;
+
+  listener.id    = id;
+  listener.event = event;
+
+RETURN_LISTENER:
+  return listener;
+}
+
+void es_remove_event_listener(EventSystem event_system, EventListener listener) {
+  if (IS_INVALID_SYSTEM(event_system) || IS_INVALID_LISTENER(listener)) {
+    return;
+  }
+
+  ESInternal *es    = get_event_system_internal(event_system);
+  EventInternal *ev = get_event(es, listener.event);
+
+  if (listener.id > ev->count) {
+    return;
+  }
+
+  if (ev->callbacks[listener.id] == NULL) {
+    return;
+  }
+
+  ev->callbacks[listener.id]   = NULL;
+  ev->free[(ev->free_count)++] = listener.id; 
+
+  if (listener.id == ev->count) {
+    ev->count -= 1;
+  }
+}
+
+void es_emit_event(EventSystem event_system, Event event, void *data) {
+  if (IS_INVALID_SYSTEM(event_system) || IS_INVALID_EVENT(event)) {
+    return;
+  }
+
+  ESInternal *es = get_event_system_internal(event_system);
+  if (event.id > es->event_count) {
+    return;
+  }
+
+  EventInternal *ev = get_event(es, event);
+  EventCallback callback;
+  for (int i = 0; i < ev->count; ++i) {
+    callback = ev->callbacks[i + 1];
+    if (!callback) {
+      continue;
+    }
+    callback(data);
+  }
+}
 
 // INTERNAL
 
diff --git a/src/event_system.h b/src/event_system.h
index 69a153c..cfd4183 100644
--- a/src/event_system.h
+++ b/src/event_system.h
@@ -25,12 +25,12 @@ struct event_listener {
   u64 id;
 };
 
-typedef void (EventCallback)(void *data);
+typedef void (*EventCallback)(void *data);
 
 EventSystem   es_init(u64 initial_event_capacity, u64 initial_listeners_capacity);
-void          es_deinit(EventSystem event_system);
+void          es_deinit(EventSystem *event_system);
 Event         es_register_event(EventSystem event_system);
 void          es_deregister_event(EventSystem event_system, Event event);
-EventListener es_add_event_listener(EventSystem event_system, Event event, EventCallback *listener);
+EventListener es_add_event_listener(EventSystem event_system, Event event, EventCallback callback);
 void          es_remove_event_listener(EventSystem event_system, EventListener listener);
 void          es_emit_event(EventSystem event_system, Event event, void *data);
diff --git a/src/main.c b/src/main.c
index 2e23d5f..a98f6c8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,6 +1,15 @@
 #include "event_system.h"
 #include <stdio.h>
 
+#define ARR_LEN(ARR) (sizeof(ARR) / sizeof(ARR[0]))
+
+void callback(void *data);
+void callback1(void *data);
+void callback2(void *data);
+void callback3(void *data);
+void callback4(void *data);
+void callback5(void *data);
+
 int main(void) {
   EventSystem es = es_init(16, 64);
 
@@ -22,7 +31,72 @@ int main(void) {
     printf("%lu\n", ev.id);
   }
 
-  es_deinit(es);
+  printf("\n");
+
+  es_deregister_event(es, (Event){ .id = 10 });
+  Event ev = es_register_event(es);
+  for (int i = 0; i < 10; ++i) {
+    EventListener listener = es_add_event_listener(es, ev, callback);
+    printf("Event: %lu, ID: %lu\n", listener.event.id, listener.id);
+  }
+
+  printf("\n");
+
+  for (int i = 5; i < 8; ++i) {
+    es_remove_event_listener(es, (EventListener){ .event = ev, .id = i });
+  }
+
+  for (int i = 0; i < 3; ++i) {
+    EventListener listener = es_add_event_listener(es, ev, callback);
+    printf("Event: %lu, ID: %lu\n", listener.event.id, listener.id);
+  }
+
+  printf("\n");
+
+  EventCallback callbacks[] = {callback1, callback2, callback3, callback4, callback5};
+  EventListener listeners[ARR_LEN(callbacks)] = {0};
+  Event ev_with_callbacks = (Event){ .id = 20 };
+  for (int i = 0; i < ARR_LEN(callbacks); ++i) {
+    listeners[i] = es_add_event_listener(es, ev_with_callbacks, callbacks[i]);
+  }
+
+  es_emit_event(es, ev_with_callbacks, (void *)0);
+
+  printf("\n");
+
+  es_remove_event_listener(es, listeners[2]);
+
+  es_emit_event(es, ev_with_callbacks, (void *)0);
+
+  printf("\n");
+
+  printf("SYSTEM: %lu\n", es.id);
+  es_deinit(&es);
+  printf("SYSTEM: %lu\n", es.id);
 
   return 0;
 }
+
+void callback(void *data) {
+  return;
+}
+
+void callback1(void *data) {
+  printf("Hello from callback1\n");
+}
+
+void callback2(void *data) {
+  printf("Hello from callback2\n");
+}
+
+void callback3(void *data) {
+  printf("Hello from callback3\n");
+}
+
+void callback4(void *data) {
+  printf("Hello from callback4\n");
+}
+
+void callback5(void *data) {
+  printf("Hello from callback5\n");
+}