diff --git a/ham.asd b/ham.asd
index 1b53089..5038a01 100644
--- a/ham.asd
+++ b/ham.asd
@@ -10,4 +10,5 @@
   :description "A framework for creating physics simulations"
   :depends-on (:sdl2)
   :components ((:file "package")
-			   (:file "drawing" :depends-on ("package"))))
+			   (:file "drawing" :depends-on ("package"))
+			   (:file "simulation" :depends-on ("package" "drawing"))))
diff --git a/simulation.lisp b/simulation.lisp
new file mode 100644
index 0000000..59db1f2
--- /dev/null
+++ b/simulation.lisp
@@ -0,0 +1,43 @@
+;; Copyright (c) Camden Dixie O'Brien
+;; SPDX-License-Identifier: AGPL-3.0-only
+
+(in-package :ham)
+
+(defclass simulation ()
+  ((update :initarg :update)
+   (render :initarg :render)
+   (state :initarg :start-state)
+   (width :initarg :width :initform 800)
+   (height :initarg :height :initform 600)
+   (running :initform nil)
+   simulation-thread))
+
+(defmethod run ((sim simulation))
+  (sdl2:make-this-thread-main
+   (lambda ()
+	 (with-slots (width height running) sim
+	   (with-graphics-context (ctx :width width :height height)
+		 (loop while running do
+		   (run-update sim (/ 1.0 60.0)) ; assume 60 Hz
+		   (run-render sim ctx)))))))
+
+(defmethod start ((sim simulation))
+  (with-slots (running simulation-thread) sim
+	(setf running t)
+	(setf simulation-thread
+		  (sb-thread:make-thread (lambda () (run sim))
+								 :name "ham-simulation-thread"))))
+
+(defmethod stop ((sim simulation))
+  (with-slots (running simulation-thread) sim
+	(setf running nil)
+	(sb-thread:join-thread simulation-thread)))
+
+(defmethod run-update ((sim simulation) dt)
+  (with-slots (update state) sim
+	(setf state (funcall update state dt))))
+
+(defmethod run-render ((sim simulation) ctx)
+  (with-slots (render state) sim
+	(let ((frame (apply render state)))
+	  (display-frame ctx frame))))