diff --git a/core/src/arch/cpu.zig b/core/src/arch/cpu.zig
index 100cd80..0130910 100644
--- a/core/src/arch/cpu.zig
+++ b/core/src/arch/cpu.zig
@@ -20,7 +20,8 @@ pub fn setupCore(allocator: *pmm.FrameAllocator) !void {
 
     const core: *arch.Core = @ptrFromInt(frame.virtualAddress(vmm.PHYSICAL_MAPPING_BASE));
     core.id = 0; // FIXME: Actually check core id
-    core.thread_list = .{};
+    core.active_thread_list = .{};
+    core.sleeping_thread_list = .{};
 
     const idle_thread = &core.idle_thread.data;
 
diff --git a/core/src/arch/x86_64/cpu.zig b/core/src/arch/x86_64/cpu.zig
index 9e806e2..a0eb369 100644
--- a/core/src/arch/x86_64/cpu.zig
+++ b/core/src/arch/x86_64/cpu.zig
@@ -1,3 +1,3 @@
 const thread = @import("../../thread.zig");
 
-pub const Core = struct { id: u32, thread_list: thread.ThreadList, current_thread: *thread.ThreadControlBlock, idle_thread: thread.ThreadList.Node };
+pub const Core = struct { id: u32, active_thread_list: thread.ThreadList, sleeping_thread_list: thread.ThreadList, current_thread: *thread.ThreadControlBlock, idle_thread: thread.ThreadList.Node };
diff --git a/core/src/main.zig b/core/src/main.zig
index dcc3df5..7b88bee 100644
--- a/core/src/main.zig
+++ b/core/src/main.zig
@@ -73,8 +73,6 @@ export fn _start(magic: u32, info: MultibootInfo) callconv(.C) noreturn {
     thread.arch.initUserRegisters(&init.regs);
     thread.arch.setArgument(&init.regs, base);
 
-    thread.addThreadToScheduler(cpu.thisCore(), init);
-
     const ctx = Context{ .allocator = &allocator, .mapper = mapper, .regs = &init.regs };
 
     multiboot.findMultibootTags(easyboot.multiboot_tag_module_t, @ptrCast(info), struct {
diff --git a/core/src/sys/sched.zig b/core/src/sys/sched.zig
index 3587af9..5ba4235 100644
--- a/core/src/sys/sched.zig
+++ b/core/src/sys/sched.zig
@@ -19,3 +19,7 @@ pub fn getPriority(_: *interrupts.InterruptStackFrame, _: *sys.Arguments, retval
     const core = cpu.thisCore();
     retval.* = core.current_thread.user_priority;
 }
+
+pub fn sleep(regs: *interrupts.InterruptStackFrame, args: *sys.Arguments, _: *isize) anyerror!void {
+    _ = thread.startSleep(regs, args.arg0);
+}
diff --git a/core/src/sys/syscall.zig b/core/src/sys/syscall.zig
index 663e1d3..7962ea8 100644
--- a/core/src/sys/syscall.zig
+++ b/core/src/sys/syscall.zig
@@ -15,7 +15,7 @@ pub const Arguments = struct {
 
 const SystemCall = *const fn (frame: *interrupts.InterruptStackFrame, args: *Arguments, retval: *isize) anyerror!void;
 
-const syscalls = [_]SystemCall{ print, mem.allocFrame, mem.lockFrame, mem.freeFrame, sched.yield, sched.setPriority, sched.getPriority };
+const syscalls = [_]SystemCall{ print, mem.allocFrame, mem.lockFrame, mem.freeFrame, sched.yield, sched.setPriority, sched.getPriority, sched.sleep };
 
 pub fn invokeSyscall(number: usize, frame: *interrupts.InterruptStackFrame, args: *Arguments, retval: *isize) void {
     if (number >= syscalls.len) {
diff --git a/core/src/thread.zig b/core/src/thread.zig
index bd02e36..af63cbe 100644
--- a/core/src/thread.zig
+++ b/core/src/thread.zig
@@ -9,6 +9,7 @@ pub const ThreadState = enum {
     Inactive,
     Running,
     Blocked,
+    Sleeping,
 };
 
 pub const ThreadControlBlock = struct {
@@ -21,6 +22,8 @@ pub const ThreadControlBlock = struct {
 
     user_priority: u8,
     current_priority: u32,
+
+    sleep_ticks: u64,
 };
 
 pub const ThreadList = std.DoublyLinkedList(ThreadControlBlock);
@@ -57,7 +60,7 @@ pub fn switchTask(regs: *interrupts.InterruptStackFrame, new_task: *ThreadContro
 }
 
 pub fn fetchNewTask(core: *cpu.arch.Core, should_idle_if_not_found: bool) ?*ThreadControlBlock {
-    const last = core.thread_list.last orelse {
+    const last = core.active_thread_list.last orelse {
         if (should_idle_if_not_found) {
             return &core.idle_thread.data;
         } else return null;
@@ -71,7 +74,7 @@ pub fn fetchNewTask(core: *cpu.arch.Core, should_idle_if_not_found: bool) ?*Thre
 }
 
 pub fn scheduleNewTask(core: *cpu.arch.Core, regs: *interrupts.InterruptStackFrame, new_thread: *ThreadControlBlock) *ThreadControlBlock {
-    if (core.thread_list.first) |first| {
+    if (core.active_thread_list.first) |first| {
         first.data.current_priority +|= 4;
     }
 
@@ -85,6 +88,11 @@ pub fn scheduleNewTask(core: *cpu.arch.Core, regs: *interrupts.InterruptStackFra
 pub fn preempt(regs: *interrupts.InterruptStackFrame) void {
     const core = cpu.thisCore();
 
+    updateSleepQueue(core);
+    while (popSleepQueue(core)) |thread| {
+        reviveThread(core, thread);
+    }
+
     core.current_thread.ticks -|= 1;
     if (core.current_thread.ticks == 0) {
         const new_thread = fetchNewTask(core, false) orelse return;
@@ -93,12 +101,81 @@ pub fn preempt(regs: *interrupts.InterruptStackFrame) void {
     }
 }
 
-var next_id: std.atomic.Value(u64) = std.atomic.Value(u64).init(1);
+pub fn block(regs: *interrupts.InterruptStackFrame) *ThreadControlBlock {
+    const core = cpu.thisCore();
 
-pub fn addThreadToScheduler(core: *cpu.arch.Core, thread: *ThreadControlBlock) void {
+    // fetchNewTask() always returns a thread if should_idle_if_not_found is set to true.
+    const new_thread = fetchNewTask(core, true) orelse unreachable;
+    const current_thread = scheduleNewTask(core, regs, new_thread);
+    current_thread.state = .Blocked;
+
+    return current_thread;
+}
+
+pub fn startSleep(regs: *interrupts.InterruptStackFrame, ticks: u64) *ThreadControlBlock {
+    const core = cpu.thisCore();
+
+    // fetchNewTask() always returns a thread if should_idle_if_not_found is set to true.
+    const new_thread = fetchNewTask(core, true) orelse unreachable;
+    const current_thread = scheduleNewTask(core, regs, new_thread);
+    current_thread.state = .Sleeping;
+    addThreadToSleepQueue(core, current_thread, ticks);
+
+    return current_thread;
+}
+
+pub fn addThreadToSleepQueue(core: *cpu.arch.Core, thread: *ThreadControlBlock, ticks: u64) void {
+    thread.sleep_ticks = ticks;
+
+    var it: ?*ThreadList.Node = core.sleeping_thread_list.first;
+    while (it) |n| : (it = n.next) {
+        if (thread.sleep_ticks <= n.data.sleep_ticks) {
+            n.data.sleep_ticks -|= thread.sleep_ticks;
+            core.sleeping_thread_list.insertBefore(n, @fieldParentPtr("data", thread));
+            return;
+        }
+        thread.sleep_ticks -|= n.data.sleep_ticks;
+    }
+
+    core.sleeping_thread_list.append(@fieldParentPtr("data", thread));
+}
+
+pub fn removeThreadFromSleepQueue(core: *cpu.arch.Core, thread: *ThreadControlBlock) void {
+    const node: *ThreadList.Node = @fieldParentPtr("data", thread);
+
+    if (node.next) |n| {
+        n.data.sleep_ticks +|= thread.sleep_ticks;
+    }
+
+    core.sleeping_thread_list.remove(node);
+
+    reviveThread(core, thread);
+}
+
+pub fn updateSleepQueue(core: *cpu.arch.Core) void {
+    const first = core.sleeping_thread_list.first orelse return;
+
+    first.data.sleep_ticks -|= 1;
+}
+
+pub fn popSleepQueue(core: *cpu.arch.Core) ?*ThreadControlBlock {
+    const first = core.sleeping_thread_list.first orelse return null;
+
+    if (first.data.sleep_ticks == 0) {
+        core.sleeping_thread_list.remove(first);
+        return &first.data;
+    }
+
+    return null;
+}
+
+pub fn reviveThread(core: *cpu.arch.Core, thread: *ThreadControlBlock) void {
+    thread.state = .Running;
     addThreadToPriorityQueue(core, thread);
 }
 
+var next_id: std.atomic.Value(u64) = std.atomic.Value(u64).init(1);
+
 pub fn createThreadControlBlock(allocator: *pmm.FrameAllocator) !*ThreadControlBlock {
     const frame = try pmm.allocFrame(allocator);
 
@@ -116,17 +193,17 @@ pub fn createThreadControlBlock(allocator: *pmm.FrameAllocator) !*ThreadControlB
 pub fn addThreadToPriorityQueue(core: *cpu.arch.Core, thread: *ThreadControlBlock) void {
     thread.current_priority = thread.user_priority;
 
-    var it: ?*ThreadList.Node = core.thread_list.first;
+    var it: ?*ThreadList.Node = core.active_thread_list.first;
     while (it) |n| : (it = n.next) {
         if (thread.current_priority <= n.data.current_priority) {
             n.data.current_priority -|= thread.current_priority;
-            core.thread_list.insertBefore(n, @fieldParentPtr("data", thread));
+            core.active_thread_list.insertBefore(n, @fieldParentPtr("data", thread));
             return;
         }
         thread.current_priority -|= n.data.current_priority;
     }
 
-    core.thread_list.append(@fieldParentPtr("data", thread));
+    core.active_thread_list.append(@fieldParentPtr("data", thread));
 }
 
 pub fn removeThreadFromPriorityQueue(core: *cpu.arch.Core, thread: *ThreadControlBlock) void {
@@ -136,5 +213,5 @@ pub fn removeThreadFromPriorityQueue(core: *cpu.arch.Core, thread: *ThreadContro
         n.data.current_priority +|= thread.current_priority;
     }
 
-    core.thread_list.remove(node);
+    core.active_thread_list.remove(node);
 }
diff --git a/system/init/kernel.zig b/system/init/kernel.zig
index 6e90838..200518b 100644
--- a/system/init/kernel.zig
+++ b/system/init/kernel.zig
@@ -6,6 +6,7 @@ const SystemCall = enum(u64) {
     Yield,
     SetPriority,
     GetPriority,
+    Sleep,
 };
 
 const SystemError = error{
@@ -49,3 +50,7 @@ pub fn setPriority(priority: u8) void {
 pub fn getPriority() u8 {
     return @truncate(@as(u64, @bitCast(syscall(.GetPriority, 0))));
 }
+
+pub fn sleep(ms: u64) void {
+    _ = syscall(.Sleep, ms);
+}
diff --git a/system/init/main.zig b/system/init/main.zig
index ed52b48..449e450 100644
--- a/system/init/main.zig
+++ b/system/init/main.zig
@@ -4,10 +4,10 @@ export fn _start(base: u64) callconv(.C) noreturn {
     kernel.print(base);
     kernel.print(kernel.getPriority());
 
-    kernel.setPriority(128);
-    kernel.print(kernel.getPriority());
+    var counter: u64 = 0;
 
-    while (true) {
-        kernel.yield();
+    while (true) : (counter += 4) {
+        kernel.sleep(1000);
+        kernel.print(counter);
     }
 }