diff --git a/.codecov.yml b/.codecov.yml
index c1c3711..69ebbfa 100644
--- a/.codecov.yml
+++ b/.codecov.yml
@@ -1,3 +1,4 @@
 ignore:
-  - catch.hpp
-  - catch_main.hpp
+  - "catch.hpp"
+  - "catch_main.hpp"
+  - "*_tests.cpp"
diff --git a/ecs.hpp b/ecs.hpp
index 60e5e16..7f31414 100644
--- a/ecs.hpp
+++ b/ecs.hpp
@@ -7,11 +7,14 @@
 #pragma once
 
 #include <cassert>
+#include <cstddef>
 #include <cstdint>
 
 #include <mutex>
 #include <limits>
+#include <utility>
 #include <functional>
+#include <type_traits>
 #include <unordered_set>
 
 // -----------------------------------------------------------------------------
@@ -25,7 +28,46 @@ namespace ecs_hpp
     class world;
     class entity;
 
-    using entity_id = std::uint64_t;
+    using family_id = std::uint16_t;
+    using entity_id = std::uint32_t;
+
+    static_assert(
+        std::is_unsigned<family_id>::value,
+        "ecs_hpp::family_id must be an unsigned integer");
+
+    static_assert(
+        std::is_unsigned<entity_id>::value,
+        "ecs_hpp::entity_id must be an unsigned integer");
+}
+
+// -----------------------------------------------------------------------------
+//
+// detail
+//
+// -----------------------------------------------------------------------------
+
+namespace ecs_hpp
+{
+    namespace detail
+    {
+        template < typename Tag = void >
+        struct type_family_base {
+            static family_id last_id_;
+        };
+
+        template < typename T >
+        class type_family : private type_family_base<> {
+        public:
+            static family_id id() noexcept {
+                static family_id self_id = ++last_id_;
+                assert(self_id > 0u && "ecs_hpp::family_id overflow");
+                return self_id;
+            }
+        };
+
+        template < typename Tag >
+        family_id type_family_base<Tag>::last_id_{0u};
+    }
 }
 
 // -----------------------------------------------------------------------------
diff --git a/ecs_tests.cpp b/ecs_tests.cpp
index 57bb26a..c1b2af1 100644
--- a/ecs_tests.cpp
+++ b/ecs_tests.cpp
@@ -12,23 +12,36 @@ namespace ecs = ecs_hpp;
 
 namespace
 {
-    struct position {
+    struct position_c {
         int x{0};
         int y{0};
 
-        position() = default;
-        position(int nx, int ny) : x(nx), y(ny) {}
+        position_c() = default;
+        position_c(int nx, int ny) : x(nx), y(ny) {}
     };
 
-    struct velocity {
+    struct velocity_c {
         int dx{0};
         int dy{0};
 
-        velocity() = default;
-        velocity(int ndx, int ndy) : dx(ndx), dy(ndy) {}
+        velocity_c() = default;
+        velocity_c(int ndx, int ndy) : dx(ndx), dy(ndy) {}
     };
 }
 
+TEST_CASE("detail") {
+    SECTION("get_type_id") {
+        REQUIRE(ecs::detail::type_family<position_c>::id() == 1u);
+        REQUIRE(ecs::detail::type_family<position_c>::id() == 1u);
+
+        REQUIRE(ecs::detail::type_family<velocity_c>::id() == 2u);
+        REQUIRE(ecs::detail::type_family<velocity_c>::id() == 2u);
+
+        REQUIRE(ecs::detail::type_family<position_c>::id() == 1u);
+        REQUIRE(ecs::detail::type_family<velocity_c>::id() == 2u);
+    }
+}
+
 TEST_CASE("world") {
     SECTION("entities") {
         {
diff --git a/scripts/upload_coverage.sh b/scripts/upload_coverage.sh
index d13a427..d7f223a 100755
--- a/scripts/upload_coverage.sh
+++ b/scripts/upload_coverage.sh
@@ -11,7 +11,7 @@ lcov -d . -z
 ctest --verbose
 
 lcov -d . -c -o "coverage.info"
-lcov -r "coverage.info" "*/usr/*" "*/catch.hpp" "*/catch_main.cpp" -o "coverage.info"
+lcov -r "coverage.info" "*/usr/*" "*/catch.hpp" "*/catch_main.cpp" "*_tests.cpp" -o "coverage.info"
 lcov -l "coverage.info"
 
 bash <(curl -s https://codecov.io/bash) || echo "Codecov did not collect coverage reports"