diff --git a/ecs/src/world.rs b/ecs/src/world.rs
index 785d7af..efd5172 100644
--- a/ecs/src/world.rs
+++ b/ecs/src/world.rs
@@ -15,15 +15,19 @@ pub struct WorldBuilder {
     pub events: Events,
     pub resources: Resources,
     archetypes: Archetypes,
-    systems: Vec<Box<dyn Fn(&mut World) -> Result<bool> + Send + Sync + 'static>>,
+    systems: Vec<(
+        u32,
+        Box<dyn Fn(&mut World) -> Result<bool> + Send + Sync + 'static>,
+    )>,
 }
 
 impl WorldBuilder {
-    pub fn add_system<F>(&mut self, f: F)
+    pub fn add_system<F>(&mut self, priority: u32, f: F)
     where
         F: Fn(&mut World) -> Result<bool> + Send + Sync + 'static,
     {
-        self.systems.push(Box::new(f));
+        self.systems.push((priority, Box::new(f)));
+        self.systems.sort_by_key(|(priority, _)| *priority);
     }
 
     pub fn add_archetype(&mut self, name: impl ToString, archetype: Archetype) {
@@ -49,7 +53,7 @@ impl WorldBuilder {
 
             start_time: Instant::now(),
 
-            systems: self.systems,
+            systems: self.systems.into_iter().map(|(_, f)| f).collect(),
         }
     }
 }