diff --git a/.gitmodules b/.gitmodules
deleted file mode 100644
index 69cf0e2..0000000
--- a/.gitmodules
+++ /dev/null
@@ -1,3 +0,0 @@
-[submodule "flecs"]
-	path = libs/flecs
-	url = https://github.com/SanderMertens/flecs.git
diff --git a/build.zig b/build.zig
index c4353a6..a8cb9df 100644
--- a/build.zig
+++ b/build.zig
@@ -7,7 +7,6 @@ pub fn build(b: *std.Build) !void {
     const module = b.createModule(.{
         .source_file = .{ .path = "src/main.zig" },
     });
-
     try b.modules.put(b.dupe("flecs-zig-ble"), module);
 
     const lib = b.addStaticLibrary(.{
@@ -16,48 +15,33 @@ pub fn build(b: *std.Build) !void {
         .target = target,
         .optimize = optimize,
     });
-
-    lib.linkLibC();
-    lib.addIncludePath(.{ .path = thisDir() ++ "/flecs" });
-    lib.addCSourceFile(.{
-        .file = .{ .path = thisDir() ++ "/flecs/flecs.c" },
-        .flags = &.{"-fno-sanitize=undefined"},
-    });
-    lib.defineCMacro("FLECS_NO_CPP", null);
-    lib.defineCMacro("FLECS_USE_OS_ALLOC", null);
-    if (@import("builtin").mode == .Debug)
-        lib.defineCMacro("FLECS_SANITIZE", null);
-
-    if (lib.target.isWindows())
-        lib.linkSystemLibraryName("ws2_32");
-
+    setupFlecs(lib);
     b.installArtifact(lib);
 
     const main_tests = b.addTest(.{
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = .{ .path = "tests/main.zig" },
+        // Has to be specified so tests can run autodoc tests from src/.
+        .main_pkg_path = .{ .path = "." },
         .target = target,
         .optimize = optimize,
     });
-
-    main_tests.linkLibC();
-    main_tests.addIncludePath(.{ .path = thisDir() ++ "/flecs" });
-    main_tests.addCSourceFile(.{
-        .file = .{ .path = thisDir() ++ "/flecs/flecs.c" },
-        .flags = &.{"-fno-sanitize=undefined"},
-    });
-    main_tests.defineCMacro("FLECS_NO_CPP", null);
-    main_tests.defineCMacro("FLECS_USE_OS_ALLOC", null);
-    main_tests.defineCMacro("FLECS_SANITIZE", null);
-
-    if (main_tests.target.isWindows())
-        main_tests.linkSystemLibraryName("ws2_32");
-
+    setupFlecs(main_tests);
     const run_main_tests = b.addRunArtifact(main_tests);
-
     const test_step = b.step("test", "Run library tests");
     test_step.dependOn(&run_main_tests.step);
 }
 
-inline fn thisDir() []const u8 {
-    return comptime std.fs.path.dirname(@src().file) orelse ".";
+fn setupFlecs(step: *std.Build.CompileStep) void {
+    step.linkLibC();
+    step.addIncludePath(.{ .path = "libs/flecs" });
+    step.addCSourceFile(.{
+        .file = .{ .path = "libs/flecs/flecs.c" },
+        .flags = &.{"-fno-sanitize=undefined"},
+    });
+    step.defineCMacro("FLECS_NO_CPP", null);
+    step.defineCMacro("FLECS_USE_OS_ALLOC", null);
+    if (@import("builtin").mode == .Debug)
+        step.defineCMacro("FLECS_SANITIZE", null);
+    if (step.target.isWindows())
+        step.linkSystemLibraryName("ws2_32");
 }
diff --git a/src/c.zig b/src/c.zig
new file mode 100644
index 0000000..5981635
--- /dev/null
+++ b/src/c.zig
@@ -0,0 +1,3 @@
+pub usingnamespace @cImport({
+    @cInclude("flecs.h");
+});
diff --git a/src/component.zig b/src/component.zig
new file mode 100644
index 0000000..e848189
--- /dev/null
+++ b/src/component.zig
@@ -0,0 +1 @@
+const c = @import("./c.zig");
diff --git a/src/entity.zig b/src/entity.zig
new file mode 100644
index 0000000..fc72f6f
--- /dev/null
+++ b/src/entity.zig
@@ -0,0 +1,16 @@
+const c = @import("./c.zig");
+
+const World = @import("./world.zig").World;
+
+pub fn Entity(comptime ctx: anytype) type {
+    return struct {
+        world: *World(ctx),
+        raw: c.ecs_entity_t,
+
+        const Self = @This();
+
+        pub fn fromRaw(world: *World(ctx), raw: c.ecs_entity_t) Self {
+            return .{ .world = world, .raw = raw };
+        }
+    };
+}
diff --git a/src/id.zig b/src/id.zig
new file mode 100644
index 0000000..e893ac7
--- /dev/null
+++ b/src/id.zig
@@ -0,0 +1,10 @@
+const c = @import("./c.zig");
+
+const World = @import("./world.zig").World;
+
+pub fn Id(comptime ctx: anytype) type {
+    return struct {
+        world: *World(ctx),
+        raw: c.ecs_id_t,
+    };
+}
diff --git a/src/iter.zig b/src/iter.zig
new file mode 100644
index 0000000..bae5853
--- /dev/null
+++ b/src/iter.zig
@@ -0,0 +1,10 @@
+const c = @import("./c.zig");
+
+const World = @import("./world.zig").World;
+
+pub fn Iter(comptime ctx: anytype) type {
+    return struct {
+        world: *World(ctx),
+        raw: c.ecs_iter_t,
+    };
+}
diff --git a/src/main.zig b/src/main.zig
index e69de29..b548ba7 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -0,0 +1,29 @@
+pub usingnamespace @import("./component.zig");
+pub usingnamespace @import("./entity.zig");
+pub usingnamespace @import("./id.zig");
+pub usingnamespace @import("./iter.zig");
+pub usingnamespace @import("./system.zig");
+pub usingnamespace @import("./world.zig");
+
+pub const c = @import("./c.zig");
+
+pub fn Context(comptime ctx: anytype) type {
+    return struct {
+        pub const Entity = @import("./entity.zig").Entity(ctx);
+        pub const Id = @import("./id.zig").Id(ctx);
+        pub const Iter = @import("./iter.zig").Iter(ctx);
+        pub const World = @import("./world.zig").World(ctx);
+
+        pub fn Lookup(comptime T: type) type {
+            _ = T; // Only necessary to create a unique type.
+            return struct {
+                pub var id: c.ecs_id_t = 0;
+            };
+        }
+    };
+}
+
+test {
+    const std = @import("std");
+    std.testing.refAllDecls(@This());
+}
diff --git a/src/system.zig b/src/system.zig
new file mode 100644
index 0000000..e69de29
diff --git a/src/util.zig b/src/util.zig
new file mode 100644
index 0000000..0ca460b
--- /dev/null
+++ b/src/util.zig
@@ -0,0 +1,9 @@
+const std = @import("std");
+
+/// Gets the simplified type name of the specified type.
+/// That is, without any namespace qualifiers.
+pub fn simpleTypeName(comptime T: type) [:0]const u8 {
+    const fullName = @typeName(T);
+    const index = std.mem.lastIndexOf(u8, fullName, ".");
+    return if (index) |i| fullName[(i + 1)..] else fullName;
+}
diff --git a/src/world.zig b/src/world.zig
new file mode 100644
index 0000000..227c888
--- /dev/null
+++ b/src/world.zig
@@ -0,0 +1,92 @@
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+
+const c = @import("./c.zig");
+const util = @import("./util.zig");
+
+pub fn World(comptime ctx: anytype) type {
+    const Lookup = @import("./main.zig").Context(ctx).Lookup;
+    const Entity = @import("./entity.zig").Entity(ctx);
+
+    return struct {
+        raw: *c.ecs_world_t,
+        allocator: Allocator,
+
+        const Self = @This();
+
+        pub fn init(alloc: Allocator) !*Self {
+            var result = try alloc.create(Self);
+            result.raw = c.ecs_init().?;
+            result.allocator = alloc;
+            return result;
+        }
+
+        pub fn initWithArgs(alloc: Allocator, args: [][*:0]u8) !*Self {
+            var result = try alloc.create(Self);
+            result.raw = c.ecs_init_w_args(args.len, args.ptr).?;
+            result.allocator = alloc;
+            return result;
+        }
+
+        pub fn deinit(self: *Self) void {
+            _ = c.ecs_fini(self.raw);
+            self.allocator.destroy(self);
+        }
+
+        pub fn progress(self: *Self, delta_time: f32) bool {
+            return c.ecs_progress(self.raw, delta_time);
+        }
+
+        pub fn entity(
+            self: *Self,
+            comptime add: []const type,
+        ) Entity {
+            var desc = std.mem.zeroes(c.ecs_entity_desc_t);
+            if (add.len > c.FLECS_ID_DESC_MAX)
+                @compileLog("add.len > FLECS_ID_DESC_MAX");
+            inline for (add, 0..) |T, i|
+                desc.add[i] = Lookup(T).id;
+            const result = c.ecs_entity_init(self.*.raw, &desc);
+            return Entity.fromRaw(self, result);
+        }
+
+        pub fn component(
+            self: *Self,
+            comptime T: type,
+        ) Entity {
+            const name = util.simpleTypeName(T);
+            const entDesc = std.mem.zeroInit(c.ecs_entity_desc_t, .{
+                .name = name,
+                .symbol = name,
+                .use_low_id = true,
+            });
+            const compDesc = std.mem.zeroInit(c.ecs_component_desc_t, .{
+                .entity = c.ecs_entity_init(self.raw, &entDesc),
+                .type = .{ .size = @sizeOf(T), .alignment = @alignOf(T) },
+            });
+            Lookup(T).id = c.ecs_component_init(self.raw, &compDesc);
+            return Entity.fromRaw(self, Lookup(T).id);
+        }
+
+        pub fn system(
+            self: *Self,
+            name: [:0]const u8,
+            callback: c.ecs_iter_action_t,
+            phase: ?Entity,
+            expr: [:0]const u8,
+        ) Entity {
+            var entDesc = std.mem.zeroes(c.ecs_entity_desc_t);
+            entDesc.name = name;
+            if (phase) |p| {
+                entDesc.add[0] = c.ecs_pair(c.EcsDependsOn, p.raw);
+                entDesc.add[1] = p.raw;
+            }
+            var sysDesc = std.mem.zeroes(c.ecs_system_desc_t);
+            sysDesc.entity = c.ecs_entity_init(self.raw, &entDesc);
+            sysDesc.query.filter.expr = expr;
+            sysDesc.callback = callback;
+            const result = c.ecs_system_init(self.raw, *sysDesc);
+            return Entity.fromRaw(self, result);
+        }
+    };
+}
diff --git a/tests/main.zig b/tests/main.zig
new file mode 100644
index 0000000..437b4fa
--- /dev/null
+++ b/tests/main.zig
@@ -0,0 +1,4 @@
+test {
+    _ = @import("../src/main.zig");
+    _ = @import("./world.zig");
+}
diff --git a/tests/util.zig b/tests/util.zig
new file mode 100644
index 0000000..a1bc44b
--- /dev/null
+++ b/tests/util.zig
@@ -0,0 +1,75 @@
+const std = @import("std");
+const expect = std.testing.expect;
+const expectEql = std.testing.expectEqual;
+const expectStrEql = std.testing.expectEqualStrings;
+
+const flecs = @import("../src/main.zig");
+const c = flecs.c;
+
+const context = flecs.Context(void);
+const Entity = context.Entity;
+const Iter = context.Iter;
+const Id = context.Id;
+
+pub const MAX_SYS_COLUMNS = 20;
+pub const MAX_ENTITIES = 256;
+pub const MAX_INVOCATIONS = 1024;
+
+pub const Probe = struct {
+    system: c.ecs_entity_t,
+    event: c.ecs_entity_t,
+    eventId: c.ecs_id_t,
+    offset: i32,
+    count: i32,
+    invoked: i32,
+    termCount: i32,
+    termIndex: i32,
+    e: [MAX_ENTITIES]c.ecs_entity_t,
+    c: [MAX_SYS_COLUMNS][MAX_INVOCATIONS]c.ecs_entity_t,
+    s: [MAX_SYS_COLUMNS][MAX_INVOCATIONS]c.ecs_entity_t,
+    param: ?*anyopaque,
+
+    pub fn init() Probe {
+        return std.mem.zeroes(Probe);
+    }
+
+    pub fn probeSystemWithContext(ctx: *Probe, it: *Iter) !void {
+        ctx.*.param = it.*.param;
+        ctx.*.system = it.*.system;
+        ctx.*.event = it.*.event;
+        ctx.*.eventId = it.*.eventId;
+        ctx.*.offset = 0;
+        ctx.*.termCount = it.*.fieldCount;
+        ctx.*.termIndex = it.*.termIndex;
+
+        for (0..ctx.*.term_count) |i| {
+            ctx.*.c[ctx.*.invoked][i] = it.*.ids[i];
+            ctx.*.s[ctx.*.invoked][i] = it.fieldSource(i + 1);
+
+            const e = it.fieldId(i + 1);
+            try expect(e != 0);
+        }
+
+        for (0..it.*.count) |i| {
+            if (i + ctx.*.count < 256) {
+                ctx.*.e[i + ctx.*.count] = it.*.entities[i];
+            } else {
+                // Can't store more than that, tests shouldn't
+                // rely on getting back more than 256 results.
+                unreachable;
+            }
+        }
+        ctx.*.count += it.*.count;
+
+        ctx.*.invoked += 1;
+    }
+
+    pub fn probeIter(it: *Iter) !void {
+        var ctx = c.ecs_get_context(it.*.world);
+        if (ctx == null) ctx = it.*.ctx;
+        if (ctx) |ct| {
+            var p: *Probe = @ptrCast(ct);
+            p.probeSystemWithContext(it);
+        }
+    }
+};
diff --git a/tests/world.zig b/tests/world.zig
new file mode 100644
index 0000000..d5895e0
--- /dev/null
+++ b/tests/world.zig
@@ -0,0 +1,71 @@
+// Reimplementations of the following tests from Flecs:
+// https://github.com/SanderMertens/flecs/blob/master/test/api/src/World.c
+
+const std = @import("std");
+const expect = std.testing.expect;
+const expectEql = std.testing.expectEqual;
+const expectStrEql = std.testing.expectEqualStrings;
+
+const util = @import("./util.zig");
+
+const flecs = @import("../src/main.zig");
+const c = flecs.c;
+
+const context = flecs.Context(void);
+const Lookup = context.Lookup;
+const World = context.World;
+const Iter = context.Iter;
+const Entity = context.Entity;
+
+const Position = struct { x: f32, y: f32 };
+const Velocity = struct { x: f32, y: f32 };
+
+fn move(it: *Iter) void {
+    var pos = it.field(Position, 1);
+    var vel = it.field(Velocity, 2);
+    util.Probe.probeIter(it);
+
+    for (0..it.count) |row| {
+        var p = &pos[row];
+        var v = &vel[row];
+        p.*.x += v.*.x * it.delta_time;
+        p.*.y += v.*.y * it.delta_time;
+    }
+}
+
+test "World_progress_w_0" {
+    var world = try World.init(std.testing.allocator);
+    defer world.deinit();
+
+    _ = world.component(Position);
+    _ = world.component(Velocity);
+
+    // const e1 = world.entity(&.{ Position, Velocity });
+
+    // // const phase = Entity.fromRaw(world, c.EcsOnUpdate);
+    // // const move_system = world.system("move", move, phase, "Position, Velocity");
+
+    // var ctx = util.Probe.init();
+    // c.ecs_set_context(world.raw, &ctx);
+
+    // // e1.set(Position, .{ 0, 0 });
+    // // e1.set(Velocity, .{ 1, 2 });
+
+    // _ = world.progress(0);
+
+    // try expectEql(ctx.count, 1);
+    // try expectEql(ctx.invoked, 1);
+    // // try expectEql(ctx.system, move_system);
+    // try expectEql(ctx.termCount, 2);
+    // try expectEql(ctx.param, null);
+
+    // try expectEql(ctx.e[0], e1.raw);
+    // try expectEql(ctx.c[0][0], Lookup(Position).id);
+    // try expectEql(ctx.c[0][1], Lookup(Velocity).id);
+    // try expectEql(ctx.s[0][0], 0);
+    // try expectEql(ctx.s[0][1], 0);
+
+    // // const p = try e1.get(Position);
+    // // try expect(p.x != 0);
+    // // try expect(p.y != 0);
+}