diff --git a/.vscode/launch.json b/.vscode/launch.json
index d8d9e70..255d999 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -1,6 +1,15 @@
 {
     "version": "0.2.0",
     "configurations": [
+        {
+            "name": "Launch Evolved All",
+            "type": "lua-local",
+            "request": "launch",
+            "program": {
+                "lua": "luajit",
+                "file": "${workspaceFolder}/develop/all.lua"
+            }
+        },
         {
             "name": "Launch Evolved Example",
             "type": "lua-local",
diff --git a/develop/all.lua b/develop/all.lua
new file mode 100644
index 0000000..e386ff5
--- /dev/null
+++ b/develop/all.lua
@@ -0,0 +1,3 @@
+require 'develop.example'
+require 'develop.unbench'
+require 'develop.untests'
diff --git a/develop/example.lua b/develop/example.lua
index 59ece27..ab3c48f 100644
--- a/develop/example.lua
+++ b/develop/example.lua
@@ -1 +1,14 @@
 local evolved = require 'evolved'
+
+local registry = evolved.registry()
+
+local fragments = {
+    position = registry:entity(),
+    velocity = registry:entity(),
+}
+
+do
+    local entity = registry:entity()
+    entity:insert(fragments.position)
+    entity:insert(fragments.velocity)
+end
diff --git a/develop/unbench.lua b/develop/unbench.lua
index 75c959b..24ca578 100644
--- a/develop/unbench.lua
+++ b/develop/unbench.lua
@@ -1,4 +1,5 @@
 local evolved = require 'evolved'
+local utilities = require 'develop.utilities'
 
 ---@param name string
 ---@param func fun(...):...
@@ -6,7 +7,7 @@ local evolved = require 'evolved'
 local function describe(name, func, ...)
     collectgarbage('stop')
 
-    print(string.format('- %s ...', name))
+    print(string.format('| unbench | %s ...', name))
 
     local start_s = os.clock()
     local start_kb = collectgarbage('count')
@@ -23,3 +24,18 @@ local function describe(name, func, ...)
 
     collectgarbage('restart')
 end
+
+describe('memory footprint of 1k entities', function()
+    local registry = evolved.registry()
+    for _ = 1, 1000 do registry:entity() end
+end)
+
+describe('memory footprint of 10k entities', function()
+    local registry = evolved.registry()
+    for _ = 1, 10000 do registry:entity() end
+end)
+
+describe('memory footprint of 100k entities', function()
+    local registry = evolved.registry()
+    for _ = 1, 100000 do registry:entity() end
+end)
diff --git a/develop/untests.lua b/develop/untests.lua
index 75c959b..48fe230 100644
--- a/develop/untests.lua
+++ b/develop/untests.lua
@@ -1,4 +1,5 @@
 local evolved = require 'evolved'
+local utilities = require 'develop.utilities'
 
 ---@param name string
 ---@param func fun(...):...
@@ -6,7 +7,7 @@ local evolved = require 'evolved'
 local function describe(name, func, ...)
     collectgarbage('stop')
 
-    print(string.format('- %s ...', name))
+    print(string.format('| untests | %s ...', name))
 
     local start_s = os.clock()
     local start_kb = collectgarbage('count')
@@ -23,3 +24,72 @@ local function describe(name, func, ...)
 
     collectgarbage('restart')
 end
+
+describe('random entity:insert', function()
+    for _ = 1, 1000 do
+        local registry = evolved.registry()
+
+        ---@type evolved.entity[]
+        local all_fragments = {}
+        local all_fragment_count = math.random(1, 10)
+        for i = 1, all_fragment_count do all_fragments[i] = registry:entity() end
+
+        for _ = 1, 100 do
+            local e1, e2 = registry:entity(), registry:entity()
+
+            ---@type evolved.entity[]
+            local insert_fragments = {}
+            local insert_fragment_count = math.random(1, 10)
+            for i = 1, insert_fragment_count do insert_fragments[i] = all_fragments[math.random(1, all_fragment_count)] end
+
+            utilities.shuffle_array(insert_fragments)
+            for _, fragment in ipairs(insert_fragments) do e1:insert(fragment) end
+
+            utilities.shuffle_array(insert_fragments)
+            for _, fragment in ipairs(insert_fragments) do e2:insert(fragment) end
+
+            assert(e1.chunk == e2.chunk)
+        end
+    end
+end)
+
+describe('random entity:remove', function()
+    for _ = 1, 1000 do
+        local registry = evolved.registry()
+
+        ---@type evolved.entity[]
+        local all_fragments = {}
+        local all_fragment_count = math.random(1, 10)
+        for i = 1, all_fragment_count do all_fragments[i] = registry:entity() end
+
+        for _ = 1, 100 do
+            local e1, e2 = registry:entity(), registry:entity()
+
+            ---@type evolved.entity[]
+            local insert_fragments = {}
+            local insert_fragment_count = math.random(1, 10)
+            for i = 1, insert_fragment_count do insert_fragments[i] = all_fragments[math.random(1, all_fragment_count)] end
+
+            ---@type evolved.entity[]
+            local remove_fragments = {}
+            local remove_fragment_count = math.random(1, 10)
+            for i = 1, remove_fragment_count do remove_fragments[i] = all_fragments[math.random(1, all_fragment_count)] end
+
+            utilities.shuffle_array(insert_fragments)
+            for _, fragment in ipairs(insert_fragments) do e1:insert(fragment) end
+
+            utilities.shuffle_array(insert_fragments)
+            for _, fragment in ipairs(insert_fragments) do e2:insert(fragment) end
+
+            assert(e1.chunk == e2.chunk)
+
+            utilities.shuffle_array(remove_fragments)
+            for _, fragment in ipairs(remove_fragments) do e1:remove(fragment) end
+
+            utilities.shuffle_array(remove_fragments)
+            for _, fragment in ipairs(remove_fragments) do e2:remove(fragment) end
+
+            assert(e1.chunk == e2.chunk)
+        end
+    end
+end)
diff --git a/develop/utilities.lua b/develop/utilities.lua
new file mode 100644
index 0000000..33cc5d5
--- /dev/null
+++ b/develop/utilities.lua
@@ -0,0 +1,11 @@
+local utilities = {}
+
+---@param vs any[]
+function utilities.shuffle_array(vs)
+    for i = 1, #vs do
+        local j = math.random(i, #vs)
+        vs[i], vs[j] = vs[j], vs[i]
+    end
+end
+
+return utilities
diff --git a/evolved.lua b/evolved.lua
index 5c5d2c6..ee981e8 100644
--- a/evolved.lua
+++ b/evolved.lua
@@ -1,4 +1,238 @@
 ---@class evolved
 local evolved = {}
 
+---
+---
+---
+---
+---
+
+---@class evolved.chunk
+---@field owner evolved.registry
+---@field parent? evolved.chunk
+---@field fragment? evolved.entity
+---@field entities evolved.entity[]
+---@field with_cache table<evolved.entity, evolved.chunk>
+---@field without_cache table<evolved.entity, evolved.chunk>
+local evolved_chunk_mt = {}
+evolved_chunk_mt.__index = evolved_chunk_mt
+
+---@class evolved.entity
+---@field owner evolved.registry
+---@field id integer
+---@field chunk? evolved.chunk
+---@field index_in_chunk? integer
+local evolved_entity_mt = {}
+evolved_entity_mt.__index = evolved_entity_mt
+
+---@class evolved.registry
+---@field nextid integer
+---@field chunks evolved.chunk[]
+local evolved_registry_mt = {}
+evolved_registry_mt.__index = evolved_registry_mt
+
+---
+---
+---
+---
+---
+
+---@param owner evolved.registry
+---@param parent? evolved.chunk
+---@param fragment? evolved.entity
+---@return evolved.chunk
+local function create_chunk(owner, parent, fragment)
+    ---@type evolved.chunk
+    local chunk = {
+        owner = owner,
+        parent = parent,
+        fragment = fragment,
+        entities = {},
+        with_cache = {},
+        without_cache = {},
+    }
+    return setmetatable(chunk, evolved_chunk_mt)
+end
+
+---@param owner evolved.registry
+---@param id integer
+local function create_entity(owner, id)
+    ---@type evolved.entity
+    local entity = {
+        owner = owner,
+        id = id,
+    }
+    return setmetatable(entity, evolved_entity_mt)
+end
+
+local function create_registry()
+    ---@type evolved.registry
+    local registry = {
+        nextid = 1,
+        chunks = {},
+    }
+
+    registry.chunks[1] = create_chunk(registry)
+
+    return setmetatable(registry, evolved_registry_mt)
+end
+
+---
+---
+--- CHUNK API
+---
+---
+
+function evolved_chunk_mt:__tostring()
+    local id, iter = '', self
+    while iter and iter.parent and iter.fragment do
+        id, iter = iter.fragment.id .. (id == '' and '' or ',') .. id, iter.parent
+    end
+    return string.format('evolved.chunk(%s)', id)
+end
+
+---@param fragment evolved.entity
+---@return evolved.chunk
+function evolved_chunk_mt:with(fragment)
+    do
+        local with_chunk = self.with_cache[fragment]
+        if with_chunk then return with_chunk end
+    end
+
+    if self.fragment and self.fragment.id == fragment.id then
+        return self
+    end
+
+    if not self.fragment or self.fragment.id < fragment.id then
+        local new_chunk = create_chunk(self.owner, self, fragment)
+        self.owner.chunks[#self.owner.chunks + 1] = new_chunk
+
+        self.with_cache[fragment] = new_chunk
+        new_chunk.without_cache[fragment] = self
+
+        return new_chunk
+    end
+
+    do
+        local sibling_chunk = self.parent
+            :with(fragment)
+            :with(self.fragment)
+
+        self.with_cache[fragment] = sibling_chunk
+
+        return sibling_chunk
+    end
+end
+
+---@param fragment evolved.entity
+---@return evolved.chunk
+function evolved_chunk_mt:without(fragment)
+    do
+        local without_chunk = self.without_cache[fragment]
+        if without_chunk then return without_chunk end
+    end
+
+    if not self.fragment or self.fragment.id < fragment.id then
+        return self
+    end
+
+    do
+        local sibling_chunk = self.parent
+            :without(fragment)
+            :with(self.fragment)
+
+        self.without_cache[fragment] = sibling_chunk
+
+        return sibling_chunk
+    end
+end
+
+---@param entity evolved.entity
+function evolved_chunk_mt:insert(entity)
+    self.entities[#self.entities + 1] = entity
+    entity.chunk, entity.index_in_chunk = self, #self.entities
+end
+
+---@param entity evolved.entity
+function evolved_chunk_mt:remove(entity)
+    local last_entity = self.entities[#self.entities]
+
+    if entity ~= last_entity then
+        self.entities[entity.index_in_chunk] = last_entity
+        last_entity.index_in_chunk = entity.index_in_chunk
+    end
+
+    self.entities[#self.entities] = nil
+    entity.chunk, entity.index_in_chunk = nil, 0
+end
+
+---
+---
+--- ENTITY API
+---
+---
+
+function evolved_entity_mt:__tostring()
+    return string.format('evolved.entity(%d)', self.id)
+end
+
+function evolved_entity_mt:destroy()
+    self.chunk:remove(self)
+end
+
+---@param fragment evolved.entity
+function evolved_entity_mt:insert(fragment)
+    local old_chunk = assert(self.chunk)
+    local new_chunk = old_chunk:with(fragment)
+
+    old_chunk:remove(self)
+    new_chunk:insert(self)
+end
+
+---@param fragment evolved.entity
+function evolved_entity_mt:remove(fragment)
+    local old_chunk = assert(self.chunk)
+    local new_chunk = old_chunk:without(fragment)
+
+    old_chunk:remove(self)
+    new_chunk:insert(self)
+end
+
+---
+---
+--- REGISTRY API
+---
+---
+
+---@return evolved.chunk
+function evolved_registry_mt:root()
+    return self.chunks[1]
+end
+
+---@return evolved.entity
+function evolved_registry_mt:entity()
+    local id = self.nextid
+    self.nextid = self.nextid + 1
+    local entity = create_entity(self, id)
+    self.chunks[1]:insert(entity)
+    return entity
+end
+
+---
+---
+--- MODULE API
+---
+---
+
+---@return evolved.registry
+function evolved.registry()
+    return create_registry()
+end
+
+---
+---
+---
+---
+---
+
 return evolved