diff --git a/crates/kernel/src/interrupt.rs b/crates/kernel/src/interrupt.rs
index 680c773..49ea814 100644
--- a/crates/kernel/src/interrupt.rs
+++ b/crates/kernel/src/interrupt.rs
@@ -1,15 +1,63 @@
-use domain::scheduler::SchedulerDecision;
+use domain::scheduler::{Scheduler, SchedulerDecision};
 use platform::Platform;
 use types::id::{CoreId, IrqId, ThreadId};
 
 use crate::Kernel;
 
 impl<P: Platform> Kernel<P> {
-    pub fn handle_tick(&mut self, _core: CoreId) -> SchedulerDecision {
-        SchedulerDecision::Continue
+    pub fn handle_tick(&mut self, core: CoreId) -> SchedulerDecision {
+        let current_tid = match self.scheduler.current(core) {
+            Some(tid) => tid,
+            None => return SchedulerDecision::Continue,
+        };
+
+        let thread = match self.threads.get_mut(current_tid) {
+            Ok(t) => t,
+            Err(_) => return SchedulerDecision::Continue,
+        };
+
+        let expired = thread.time_slice_mut().tick();
+        if expired {
+            thread.time_slice_mut().reset();
+            let priority = thread.priority();
+            if thread.preempt().is_err() {
+                return SchedulerDecision::Continue;
+            }
+            self.scheduler.add(current_tid, priority, core);
+            match self.scheduler.next(core) {
+                Some(next) => {
+                    if self.threads.get_mut(next).and_then(|t| t.set_running(core)).is_ok() {
+                        SchedulerDecision::Preempt(next)
+                    } else {
+                        let _ = self.threads.get_mut(current_tid).map(|t| t.set_running(core));
+                        SchedulerDecision::Continue
+                    }
+                }
+                None => {
+                    let _ = self.threads.get_mut(current_tid).map(|t| t.set_running(core));
+                    SchedulerDecision::Continue
+                }
+            }
+        } else {
+            self.scheduler.tick(core, current_tid)
+        }
     }
 
-    pub fn handle_interrupt(&mut self, _irq: IrqId) -> Option<ThreadId> {
-        None
+    pub fn handle_interrupt(&mut self, irq: IrqId) -> Option<ThreadId> {
+        self.platform.mask_irq(irq);
+
+        let tid = self.irqs.owner(irq)?;
+        let thread = self.threads.get_mut(tid).ok()?;
+
+        if !matches!(thread.state(), domain::thread::ThreadState::Blocked(_)) {
+            return None;
+        }
+
+        let priority = thread.priority();
+        let core = self.platform.core_id();
+        let _ = thread.unblock();
+        self.scheduler.add(tid, priority, core);
+
+        Some(tid)
     }
 }
diff --git a/crates/kernel/src/lib.rs b/crates/kernel/src/lib.rs
index ac7539a..12e886f 100644
--- a/crates/kernel/src/lib.rs
+++ b/crates/kernel/src/lib.rs
@@ -152,4 +152,41 @@ impl<P: Platform> Kernel<P> {
         let cap = Capability::new(resource, permissions, Generation::initial());
         self.processes.get_mut(to)?.capabilities_mut().insert(cap)
     }
+
+    #[cfg(test)]
+    pub fn spawn_thread_for_test(
+        &mut self,
+        pid: ProcessId,
+        priority: Priority,
+        time_slice: TimeSlice,
+    ) -> ThreadId {
+        use domain::scheduler::Scheduler;
+        let tid = self.threads.spawn(pid, priority, time_slice, None).expect("spawn");
+        let _ = self.processes.get_mut(pid).map(|p| p.add_thread(tid));
+        let core = self.platform.core_id();
+        self.scheduler.add(tid, priority, core);
+        tid
+    }
+
+    #[cfg(test)]
+    pub fn register_irq_for_test(&mut self, irq: types::id::IrqId, thread: ThreadId) {
+        let _ = self.irqs.register(irq, thread);
+    }
+
+    #[cfg(test)]
+    pub fn block_thread_for_test(
+        &mut self,
+        tid: ThreadId,
+        reason: domain::thread::BlockReason,
+    ) {
+        use domain::scheduler::Scheduler;
+        let core = self.platform.core_id();
+        if let Ok(t) = self.threads.get_mut(tid) {
+            if matches!(t.state(), ThreadState::Ready) {
+                let _ = t.set_running(core);
+            }
+            let _ = t.block(reason);
+        }
+        self.scheduler.remove(tid);
+    }
 }
diff --git a/crates/kernel/src/tests/mod.rs b/crates/kernel/src/tests/mod.rs
index 2a94df6..df62df3 100644
--- a/crates/kernel/src/tests/mod.rs
+++ b/crates/kernel/src/tests/mod.rs
@@ -1,5 +1,6 @@
 mod exit;
 mod simple;
+mod tick;
 
 use domain::memory::page_pool::PagePool;
 use platform::Platform;
diff --git a/crates/kernel/src/tests/tick.rs b/crates/kernel/src/tests/tick.rs
new file mode 100644
index 0000000..3d9cb80
--- /dev/null
+++ b/crates/kernel/src/tests/tick.rs
@@ -0,0 +1,55 @@
+use super::*;
+use domain::scheduler::SchedulerDecision;
+use types::id::{CoreId, IrqId, ThreadId};
+use types::time::TimeSlice;
+
+#[test]
+fn tick_continues_when_time_remaining() {
+    let (mut k, _) = kernel_with_process();
+    let decision = k.handle_tick(CoreId::from_raw(0));
+    assert!(matches!(decision, SchedulerDecision::Continue));
+}
+
+#[test]
+fn tick_preempts_when_time_expired_and_other_thread_ready() {
+    let mut k = test_kernel();
+    let mock = MockPlatform::new(1);
+    let pool = PagePool::new(PhysicalAddress::from_raw(0x8000_0000), 1024);
+    let mut k = Kernel::new(mock, pool);
+
+    // Boot with quantum=2 so it expires after 2 ticks
+    let (pid, tid1) = k.boot(Priority::new(16).unwrap(), TimeSlice::new(2)).unwrap();
+
+    // Spawn a second thread so scheduler has someone to switch to
+    let tid2 = k.spawn_thread_for_test(pid, Priority::new(16).unwrap(), TimeSlice::new(100));
+
+    // First tick: time remaining
+    let d1 = k.handle_tick(CoreId::from_raw(0));
+    assert!(matches!(d1, SchedulerDecision::Continue));
+
+    // Second tick: time expired, should preempt
+    let d2 = k.handle_tick(CoreId::from_raw(0));
+    assert!(matches!(d2, SchedulerDecision::Preempt(_)));
+}
+
+#[test]
+fn interrupt_unknown_irq_returns_none() {
+    let (mut k, _) = kernel_with_process();
+    assert!(k.handle_interrupt(IrqId::from_raw(99)).is_none());
+}
+
+#[test]
+fn interrupt_unblocks_registered_thread() {
+    let (mut k, _) = kernel_with_process();
+    let tid = ThreadId::from_raw(0);
+    let irq = IrqId::from_raw(5);
+
+    // Register and block the thread on this IRQ
+    k.register_irq_for_test(irq, tid);
+    k.block_thread_for_test(tid, domain::thread::BlockReason::WaitingForInterrupt(
+        types::bounded::CapSlot::new(0).unwrap()
+    ));
+
+    let result = k.handle_interrupt(irq);
+    assert_eq!(result, Some(tid));
+}