diff --git a/becs3.h b/becs3.h
index 05a01b0..c79ccaf 100644
--- a/becs3.h
+++ b/becs3.h
@@ -1,8 +1,15 @@
 /*
  * Usage:
- * Define BECS_IMPLEMENTATION in exactly _one_ file before including this file
  *
- * Eg:
+ * Define BECS_MAX_ENTITIES and BECS_MAX_COMPONENTS. Otherwise they will have
+ * the following defaults:
+ *
+ * #define BECS_MAX_ENTITIES 4096
+ * #define BECS_MAX_COMPONENTS 64
+ *
+ * Then define BECS_IMPLEMENTATION in exactly _one_ file before including this
+ * file as follows:
+ *
  * #define BECS_IMPLEMENTATION
  * #include "becs.h"
  */
@@ -28,6 +35,10 @@ typedef struct BECS_ECS BECS_ECS;
 typedef uint32_t BECS_Entity;
 typedef uint32_t BECS_ComponentID;
 
+size_t BECS_GetMinMemoryArenaSize(size_t *componentSizes, size_t arrayLength);
+BECS_ECS BECS_InitECS(void *memory, size_t size);
+void BECS_ResetECS(BECS_ECS *ecs);
+
 BECS_Entity BECS_EntityCreate(BECS_ECS *ecs);
 void BECS_EntityDestroy(BECS_ECS *ecs, BECS_Entity entity);
 bool BECS_IsEntityAlive(BECS_ECS *ecs, BECS_Entity entity);
@@ -35,7 +46,7 @@ bool BECS_IsEntityAlive(BECS_ECS *ecs, BECS_Entity entity);
 BECS_ComponentID BECS_ComponentRegister(BECS_ECS *ecs, size_t componentSize, size_t maximumComponentCount);
 void *BECS_ComponentAdd(BECS_ECS *ecs, BECS_Entity entity, BECS_ComponentID componentId);
 void BECS_ComponentRemove(BECS_ECS *ecs, BECS_Entity entity, BECS_ComponentID componentId);
-void* BECS_ComponentGet(BECS_ECS *ecs, BECS_Entity entity, BECS_ComponentID componentId);
+void *BECS_ComponentGet(BECS_ECS *ecs, BECS_Entity entity, BECS_ComponentID componentId);
 bool BECS_ComponentHas(BECS_ECS *ecs, BECS_Entity entity, BECS_ComponentID componentId);
 
 #ifdef BECS_IMPLEMENTATION
@@ -72,6 +83,7 @@ struct BECS_ECS {
     BECS_Arena arena;
 
     /* Entity Management */
+    BECS_Entity nextEntity;
     uint32_t entityCount;
     BECS_Signature entitySignatures[BECS_MAX_ENTITIES];
     bool aliveEntites[BECS_MAX_ENTITIES];
@@ -90,12 +102,12 @@ static BECS_Signature BECS_SignatureSet(BECS_Signature sig, BECS_ComponentID com
     return sig | (1ULL << componentId);
 }
 
-static bool ecs_signature_has(BECS_Signature sig, BECS_ComponentID component_id)
+static bool BECS_SignatureHas(BECS_Signature sig, BECS_ComponentID component_id)
 {
     return (sig & (1ULL << component_id)) != 0;
 }
 
-static bool ecs_signature_matches(BECS_Signature entitySig, BECS_Signature querySig)
+static bool BECS_SignatureMatches(BECS_Signature entitySig, BECS_Signature querySig)
 {
     return (entitySig & querySig) == querySig;
 }
@@ -197,6 +209,29 @@ static bool BECS_ComponentPoolHas(BECS_ComponentPool *pool, BECS_Entity entity)
     return pool->sparseArray[entity] != UINT32_MAX;
 }
 
+/* Helper API Functions */
+
+size_t BECS_GetMinMemoryArenaSize(size_t *componentSizes, size_t arrayLength)
+{
+    assert(arrayLength < BECS_MAX_COMPONENTS);
+    size_t totalSize = 0;
+    totalSize += sizeof(BECS_ECS);
+    totalSize += sizeof(BECS_ComponentPool) * BECS_MAX_COMPONENTS;
+    totalSize += sizeof(BECS_Entity) * BECS_MAX_ENTITIES * BECS_MAX_COMPONENTS;
+
+    size_t sumCompSizes = 0;
+    uint32_t i;
+    for (i = 0; i < arrayLength; i++)
+    {
+        sumCompSizes += componentSizes[i];
+    }
+
+    sumCompSizes *= BECS_MAX_ENTITIES;
+    totalSize += sumCompSizes;
+
+    return totalSize;
+}
+
 /* World API Functions */
 
 BECS_ECS BECS_InitECS(void *memory, size_t size)
@@ -205,9 +240,10 @@ BECS_ECS BECS_InitECS(void *memory, size_t size)
     ecs.arena = BECS_CreateArena(memory, size);
     ecs.entityCount = 0;
     memset(ecs.entitySignatures, 0, sizeof(BECS_Signature) * BECS_MAX_ENTITIES);
-    memset(ecs.aliveEntites, 0, sizeof(bool) * BECS_MAX_ENTITIES);
+    memset(ecs.aliveEntites, false, sizeof(bool) * BECS_MAX_ENTITIES);
     memset(ecs.freeEntities, BECS_NULL_ENTITY, sizeof(BECS_Entity) * BECS_MAX_ENTITIES);
     ecs.freeEntityCount = 0;
+    ecs.nextEntity = 0;
 
     ecs.componentTypeCount = 0;
     uint32_t i;
@@ -225,9 +261,10 @@ void BECS_ResetECS(BECS_ECS *ecs)
     ecs->arena = BECS_CreateArena(ecs->arena.memory, ecs->arena.capacity);
     ecs->entityCount = 0;
     memset(ecs->entitySignatures, 0, sizeof(BECS_Signature) * BECS_MAX_ENTITIES);
-    memset(ecs->aliveEntites, 0, sizeof(bool) * BECS_MAX_ENTITIES);
+    memset(ecs->aliveEntites, false, sizeof(bool) * BECS_MAX_ENTITIES);
     memset(ecs->freeEntities, BECS_NULL_ENTITY, sizeof(BECS_Entity) * BECS_MAX_ENTITIES);
     ecs->freeEntityCount = 0;
+    ecs->nextEntity = 0;
 
     ecs->componentTypeCount = 0;
     uint32_t i;
@@ -240,20 +277,60 @@ void BECS_ResetECS(BECS_ECS *ecs)
 
 /* Entity API Functions */
 
-/* TODO: Implement Entity API Functions
-
 BECS_Entity BECS_EntityCreate(BECS_ECS *ecs)
 {
+    BECS_Entity entity = BECS_NULL_ENTITY;
+
+    if (ecs->nextEntity + 1 > BECS_NULL_ENTITY)
+    {
+        return entity;
+    }
+
+    if (ecs->freeEntityCount)
+    {
+        /* Pop entity off the back of the free list */
+        entity = ecs->freeEntities[--ecs->freeEntityCount];
+        ecs->entitySignatures[entity] = 0;
+        ecs->aliveEntites[entity] = true;
+        return entity;
+    }
+
+    entity = ecs->nextEntity;
+    ecs->aliveEntites[entity] = true;
+    ecs->entitySignatures[entity] = 0;
+    ecs->nextEntity++;
+    ecs->entityCount++;
+    return entity;
 }
 
 void BECS_EntityDestroy(BECS_ECS *ecs, BECS_Entity entity)
 {
+    if (!ecs->aliveEntites[entity])
+    {
+        return;
+    }
+
+    uint32_t i;
+    for (i = 0; i < BECS_MAX_COMPONENTS; i++)
+    {
+        BECS_Signature sig = ecs->entitySignatures[entity];
+        if (BECS_SignatureHas(sig, i))
+        {
+            BECS_ComponentRemove(ecs, entity, i);
+        }
+    }
+
+    ecs->aliveEntites[entity] = false;
+    ecs->entitySignatures[entity] = 0;
+    ecs->freeEntities[ecs->freeEntityCount] = entity;
+    ecs->entityCount--;
+    ecs->freeEntityCount++;
 }
 
 bool BECS_IsEntityAlive(BECS_ECS *ecs, BECS_Entity entity)
 {
+    return ecs->aliveEntites[entity];
 }
-*/
 
 /* Component API Functions */
 
@@ -290,7 +367,7 @@ void BECS_ComponentRemove(BECS_ECS *ecs, BECS_Entity entity, BECS_ComponentID co
     ecs->entitySignatures[entity] &= ~(1ULL << componentId);
 }
 
-void* BECS_ComponentGet(BECS_ECS *ecs, BECS_Entity entity, BECS_ComponentID componentId)
+void *BECS_ComponentGet(BECS_ECS *ecs, BECS_Entity entity, BECS_ComponentID componentId)
 {
 
     if (!ecs->aliveEntites[entity])
@@ -306,7 +383,7 @@ bool BECS_ComponentHas(BECS_ECS *ecs, BECS_Entity entity, BECS_ComponentID compo
     {
         return false;
     }
-    return ecs_signature_has(ecs->entitySignatures[entity], componentId);
+    return BECS_SignatureHas(ecs->entitySignatures[entity], componentId);
 }
 
 #endif /* BECS_IMPLEMENTATION */