diff --git a/CREDITS.md b/CREDITS.md
index 8353b9cb40..d2ac81cd30 100644
--- a/CREDITS.md
+++ b/CREDITS.md
@@ -5,6 +5,7 @@
 * hecs
 * legion_transform
 * wgpu-rs examples
+* yaks: ArchetypeSet, borrowed some ideas from their scheduler implementation 
 
 ## Inspiration
 
diff --git a/crates/bevy_ecs/Cargo.toml b/crates/bevy_ecs/Cargo.toml
index cacd4672ff..04bfcf7641 100644
--- a/crates/bevy_ecs/Cargo.toml
+++ b/crates/bevy_ecs/Cargo.toml
@@ -12,4 +12,6 @@ profiler = []
 [dependencies]
 hecs = { path = "hecs", features = ["macros", "serialize"] }
 rand = "0.7.2"
-rayon = "1.3"
\ No newline at end of file
+rayon = "1.3"
+crossbeam-channel = "0.4.2"
+fixedbitset = "0.3.0"
\ No newline at end of file
diff --git a/crates/bevy_ecs/src/executor.rs b/crates/bevy_ecs/src/executor.rs
new file mode 100644
index 0000000000..637a867254
--- /dev/null
+++ b/crates/bevy_ecs/src/executor.rs
@@ -0,0 +1,369 @@
+use crate::{system::ThreadLocalExecution, Resources, Schedule, System};
+use crossbeam_channel::{Receiver, Sender};
+use fixedbitset::FixedBitSet;
+use hecs::{Access, Query, World};
+use rayon::ScopeFifo;
+use std::sync::{Arc, Mutex};
+
+#[derive(Default)]
+pub struct Executor {
+    stages: Vec<ExecutorStage>,
+}
+
+impl Executor {
+    pub fn prepare(&mut self, schedule: &mut Schedule, world: &World) {
+        // TODO: if world archetype generation hasnt changed, dont update here
+
+        let mut executor_stages = vec![ExecutorStage::default(); schedule.stage_order.len()];
+        for (stage_index, stage_name) in schedule.stage_order.iter().enumerate() {
+            let executor_stage = &mut executor_stages[stage_index];
+            // ensure finished dependencies has the required number of bits
+            if let Some(systems) = schedule.stages.get(stage_name) {
+                executor_stage.prepare(world, systems);
+            }
+        }
+
+        self.stages = executor_stages;
+    }
+
+    pub fn run(&mut self, schedule: &mut Schedule, world: &mut World, resources: &mut Resources) {
+        for (stage_name, executor_stage) in schedule.stage_order.iter().zip(self.stages.iter_mut())
+        {
+            if let Some(stage_systems) = schedule.stages.get_mut(stage_name) {
+                executor_stage.run(world, resources, stage_systems);
+            }
+        }
+    }
+}
+
+#[derive(Clone)]
+pub struct ExecutorStage {
+    /// each system's set of dependencies
+    system_dependencies: Vec<FixedBitSet>,
+    /// each system's dependents (the systems that can't run until this system has run)
+    system_dependents: Vec<Vec<usize>>,
+
+    /// the currently finished systems
+    finished_systems: FixedBitSet,
+    running_systems: FixedBitSet,
+
+    sender: Sender<usize>,
+    receiver: Receiver<usize>,
+}
+
+impl Default for ExecutorStage {
+    fn default() -> Self {
+        let (sender, receiver) = crossbeam_channel::unbounded();
+        Self {
+            system_dependents: Default::default(),
+            system_dependencies: Default::default(),
+            finished_systems: Default::default(),
+            running_systems: Default::default(),
+            sender,
+            receiver,
+        }
+    }
+}
+
+impl ExecutorStage {
+    pub fn prepare(&mut self, world: &World, systems: &Vec<Arc<Mutex<Box<dyn System>>>>) {
+        self.system_dependencies = vec![FixedBitSet::with_capacity(systems.len()); systems.len()];
+        self.system_dependents = vec![Vec::new(); systems.len()];
+        self.finished_systems.grow(systems.len());
+        self.running_systems.grow(systems.len());
+
+        // update each system's archetype access to latest world archetypes
+        for system in systems.iter() {
+            let mut system = system.lock().unwrap();
+            system.update_archetype_access(world);
+        }
+
+        let mut current_archetype_access = ArchetypeAccess::default();
+        for (system_index, system) in systems.iter().enumerate() {
+            let system = system.lock().unwrap();
+            if let Some(archetype_access) = system.get_archetype_access() {
+                // TODO: check if thread local and add full sync
+                // if any system before this one conflicts, check all systems that came before for compatibility
+                if current_archetype_access.is_compatible(archetype_access) == false {
+                    for earlier_system_index in 0..system_index {
+                        let earlier_system = systems[earlier_system_index].lock().unwrap();
+                        if let Some(earlier_archetype_access) =
+                            earlier_system.get_archetype_access()
+                        {
+                            // if earlier system is incompatible, make the current system dependent
+                            if earlier_archetype_access.is_compatible(archetype_access) == false {
+                                self.system_dependents[earlier_system_index].push(system_index);
+                                self.system_dependencies[system_index].insert(earlier_system_index);
+                            }
+                        }
+                    }
+                }
+
+                current_archetype_access.union(archetype_access);
+            }
+        }
+    }
+
+    pub fn run_ready_systems<'run>(
+        &mut self,
+        systems: &[Arc<Mutex<Box<dyn System>>>],
+        scope: &ScopeFifo<'run>,
+        world: &'run World,
+        resources: &'run Resources,
+    ) {
+        for i in 0..systems.len() {
+            Self::try_run_system(
+                systems,
+                i,
+                &mut self.running_systems,
+                &self.finished_systems,
+                &self.system_dependencies,
+                &self.sender,
+                scope,
+                world,
+                resources,
+            );
+        }
+    }
+
+    #[inline]
+    pub fn try_run_system<'run>(
+        systems: &[Arc<Mutex<Box<dyn System>>>],
+        system_index: usize,
+        running_systems: &mut FixedBitSet,
+        finished_systems: &FixedBitSet,
+        system_dependencies: &[FixedBitSet],
+        sender: &Sender<usize>,
+        scope: &ScopeFifo<'run>,
+        world: &'run World,
+        resources: &'run Resources,
+    ) {
+        if running_systems.contains(system_index) {
+            return;
+        }
+
+        // if all system dependencies are finished, queue up the system to run
+        if system_dependencies[system_index].is_subset(&finished_systems) {
+            let system = systems[system_index].clone();
+            let sender = sender.clone();
+            running_systems.insert(system_index);
+            scope.spawn_fifo(move |_| {
+                let mut system = system.lock().unwrap();
+                system.run(world, resources);
+                sender.send(system_index).unwrap();
+            })
+        }
+    }
+
+    pub fn run(
+        &mut self,
+        world: &mut World,
+        resources: &mut Resources,
+        systems: &[Arc<Mutex<Box<dyn System>>>],
+    ) {
+        self.finished_systems.clear();
+        self.running_systems.clear();
+        {
+            let world = &*world;
+            let resources = &*resources;
+
+            rayon::scope_fifo(move |scope| {
+                self.run_ready_systems(systems, scope, world, resources);
+                loop {
+                    if self.finished_systems.count_ones(..) == systems.len() {
+                        break;
+                    }
+
+                    let finished_system = self.receiver.recv().unwrap();
+                    self.finished_systems.insert(finished_system);
+                    for dependent_system in self.system_dependents[finished_system].iter() {
+                        Self::try_run_system(
+                            systems,
+                            *dependent_system,
+                            &mut self.running_systems,
+                            &self.finished_systems,
+                            &self.system_dependencies,
+                            &self.sender,
+                            scope,
+                            world,
+                            resources,
+                        );
+                    }
+                }
+            });
+        }
+
+        // "flush"
+        // NOTE: when this is made parallel a full sync is required here
+        for system in systems.iter() {
+            let mut system = system.lock().unwrap();
+            match system.thread_local_execution() {
+                ThreadLocalExecution::NextFlush => system.run_thread_local(world, resources),
+                ThreadLocalExecution::Immediate => {
+                    // TODO: this should happen immediately after thread local systems
+                    system.run_thread_local(world, resources)
+                }
+            }
+        }
+    }
+}
+
+// credit to Ratysz from the Yaks codebase
+#[derive(Default)]
+pub struct ArchetypeAccess {
+    pub immutable: FixedBitSet,
+    pub mutable: FixedBitSet,
+}
+
+impl ArchetypeAccess {
+    pub fn is_compatible(&self, other: &ArchetypeAccess) -> bool {
+        self.mutable.is_disjoint(&other.mutable)
+            && self.mutable.is_disjoint(&other.immutable)
+            && self.immutable.is_disjoint(&other.mutable)
+    }
+
+    pub fn union(&mut self, other: &ArchetypeAccess) {
+        self.mutable.union_with(&other.mutable);
+        self.immutable.union_with(&other.immutable);
+    }
+
+    pub fn set_bits_for_query<Q>(&mut self, world: &World)
+    where
+        Q: Query,
+    {
+        self.immutable.clear();
+        self.mutable.clear();
+        let iterator = world.archetypes();
+        let bits = iterator.len();
+        self.immutable.grow(bits);
+        self.mutable.grow(bits);
+        iterator
+            .enumerate()
+            .filter_map(|(index, archetype)| archetype.access::<Q>().map(|access| (index, access)))
+            .for_each(|(archetype, access)| match access {
+                Access::Read => self.immutable.set(archetype, true),
+                Access::Write => self.mutable.set(archetype, true),
+                Access::Iterate => (),
+            });
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Executor;
+    use crate::{IntoQuerySystem, Query, Res, Resources, Schedule, World};
+    use fixedbitset::FixedBitSet;
+    use std::sync::{Arc, Mutex};
+
+    #[derive(Default)]
+    struct Counter {
+        count: Arc<Mutex<usize>>,
+    }
+
+    fn read_u32(counter: Res<Counter>, _query: Query<&u32>) {
+        let mut count = counter.count.lock().unwrap();
+        assert!(
+            *count < 2,
+            "read_32 should run be one of the first two systems to run"
+        );
+        *count += 1;
+    }
+
+    fn write_float(counter: Res<Counter>, _query: Query<&f32>) {
+        let mut count = counter.count.lock().unwrap();
+        assert!(
+            *count < 2,
+            "write_float should run be one of the first two systems to run"
+        );
+        *count += 1;
+    }
+
+    fn read_u32_write_u64(counter: Res<Counter>, _query: Query<(&u32, &mut u64)>) {
+        let mut count = counter.count.lock().unwrap();
+        assert_eq!(
+            *count, 2,
+            "read_u32_write_u64 should always be the third system to run"
+        );
+        *count += 1;
+    }
+
+    fn read_u64(counter: Res<Counter>, _query: Query<&u64>) {
+        let mut count = counter.count.lock().unwrap();
+        assert_eq!(
+            *count, 3,
+            "read_u64 should always be the fourth system to run"
+        );
+        *count += 1;
+    }
+
+    fn write_u64(counter: Res<Counter>, _query: Query<&mut u64>) {
+        let mut count = counter.count.lock().unwrap();
+        assert_eq!(
+            *count, 4,
+            "write_u64 should always be the fifth system to run"
+        );
+        *count += 1;
+    }
+
+    #[test]
+    fn schedule() {
+        let mut world = World::new();
+        let mut resources = Resources::default();
+        resources.insert(Counter::default());
+
+        world.spawn((1.0f32,));
+        world.spawn((1u32, 1u64));
+        world.spawn((2u32,));
+
+        let mut schedule = Schedule::default();
+        schedule.add_stage("A");
+        schedule.add_stage("B");
+
+        schedule.add_system_to_stage("A", read_u32.system());
+        schedule.add_system_to_stage("A", write_float.system());
+        schedule.add_system_to_stage("A", read_u32_write_u64.system());
+        schedule.add_system_to_stage("A", read_u64.system());
+        schedule.add_system_to_stage("B", write_u64.system());
+
+        let mut executor = Executor::default();
+        executor.prepare(&mut schedule, &world);
+
+        assert_eq!(
+            executor.stages[0].system_dependents,
+            vec![vec![2], vec![], vec![3], vec![]]
+        );
+        assert_eq!(executor.stages[1].system_dependents, vec![vec![]]);
+
+        let stage_0_len = executor.stages[0].system_dependencies.len();
+        let mut read_u32_write_u64_deps = FixedBitSet::with_capacity(stage_0_len);
+        read_u32_write_u64_deps.insert(0);
+        let mut read_u64_deps = FixedBitSet::with_capacity(stage_0_len);
+        read_u64_deps.insert(2);
+
+        assert_eq!(
+            executor.stages[0].system_dependencies,
+            vec![
+                FixedBitSet::with_capacity(stage_0_len),
+                FixedBitSet::with_capacity(stage_0_len),
+                read_u32_write_u64_deps,
+                read_u64_deps,
+            ]
+        );
+
+        assert_eq!(
+            executor.stages[1].system_dependencies,
+            vec![
+                FixedBitSet::with_capacity(1),
+            ]
+        );
+
+        executor.run(&mut schedule, &mut world, &mut resources);
+
+        let counter = resources.get::<Counter>().unwrap();
+        assert_eq!(
+            *counter.count.lock().unwrap(),
+            5,
+            "counter should have been incremented once for each system"
+        );
+    }
+}
diff --git a/crates/bevy_ecs/src/into_system.rs b/crates/bevy_ecs/src/into_system.rs
index e7372f1802..48b3980ede 100644
--- a/crates/bevy_ecs/src/into_system.rs
+++ b/crates/bevy_ecs/src/into_system.rs
@@ -1,7 +1,7 @@
 use crate::{
     resource_query::{FetchResource, ResourceQuery, UnsafeClone},
     system::{System, SystemId, ThreadLocalExecution},
-    Commands, Resources, Res,
+    Commands, Resources, executor::ArchetypeAccess,
 };
 use core::marker::PhantomData;
 use hecs::{
@@ -9,10 +9,11 @@ use hecs::{
 };
 use std::borrow::Cow;
 
-pub struct SystemFn<F, Init>
+pub struct SystemFn<F, Init, SetArchetypeAccess>
 where
     F: FnMut(Commands, &World, &Resources) + Send + Sync,
     Init: FnMut(&mut Resources) + Send + Sync,
+    SetArchetypeAccess: FnMut(&World, &mut ArchetypeAccess) + Send + Sync,
 {
     pub func: F,
     pub init_func: Init,
@@ -20,18 +21,29 @@ where
     pub thread_local_execution: ThreadLocalExecution,
     pub name: Cow<'static, str>,
     pub id: SystemId,
+    pub archetype_access: ArchetypeAccess,
+    pub set_archetype_access: SetArchetypeAccess,
     // TODO: add dependency info here
 }
 
-impl<F, Init> System for SystemFn<F, Init>
+impl<F, Init, SetArchetypeAccess> System for SystemFn<F, Init, SetArchetypeAccess>
 where
     F: FnMut(Commands, &World, &Resources) + Send + Sync,
     Init: FnMut(&mut Resources) + Send + Sync,
+    SetArchetypeAccess: FnMut(&World, &mut ArchetypeAccess) + Send + Sync,
 {
     fn name(&self) -> Cow<'static, str> {
         self.name.clone()
     }
 
+    fn update_archetype_access(&mut self, world: &World) {
+        (self.set_archetype_access)(world, &mut self.archetype_access);
+    }
+
+    fn get_archetype_access(&self) -> Option<&ArchetypeAccess> {
+        Some(&self.archetype_access)
+    }
+
     fn thread_local_execution(&self) -> ThreadLocalExecution {
         self.thread_local_execution
     }
@@ -95,6 +107,12 @@ macro_rules! impl_into_foreach_system {
                     init_func: move |resources| {
                         <($($resource,)*)>::initialize(resources, Some(id));
                     },
+                    archetype_access: ArchetypeAccess::default(),
+                    set_archetype_access: |world, archetype_access| {
+                        for archetype in world.archetypes() {
+                           archetype_access.set_bits_for_query::<($($component,)*)>(world);
+                        }
+                    },
                 })
             }
         }
@@ -165,6 +183,12 @@ macro_rules! impl_into_query_system {
                     init_func: move |resources| {
                         <($($resource,)*)>::initialize(resources, Some(id));
                     },
+                    archetype_access: ArchetypeAccess::default(),
+                    set_archetype_access: |world, archetype_access| {
+                        for archetype in world.archetypes() {
+                           $(archetype_access.set_bits_for_query::<$query>(world);)* 
+                        }
+                    },
                 })
             }
         }
@@ -311,4 +335,9 @@ where
     fn id(&self) -> SystemId {
         self.id
     }
+    fn update_archetype_access(&mut self, _world: &World) {
+    }
+    fn get_archetype_access(&self) -> Option<&ArchetypeAccess> {
+        None
+    }
 }
diff --git a/crates/bevy_ecs/src/lib.rs b/crates/bevy_ecs/src/lib.rs
index 16c4624501..34708e21d2 100644
--- a/crates/bevy_ecs/src/lib.rs
+++ b/crates/bevy_ecs/src/lib.rs
@@ -1,6 +1,7 @@
 pub use hecs::{Query as HecsQuery, *};
 
 mod commands;
+mod executor;
 mod into_system;
 #[cfg(feature = "profiler")]
 pub mod profiler;
@@ -15,5 +16,6 @@ pub use into_system::{IntoForEachSystem, IntoQuerySystem, Query, ThreadLocalSyst
 pub use resource_query::{FetchResource, Local, Res, ResMut, ResourceQuery};
 pub use resources::{FromResources, Resource, Resources};
 pub use schedule::Schedule;
+pub use executor::Executor;
 pub use system::{System, SystemId};
 pub use world_builder::{WorldBuilder, WorldBuilderSource};
diff --git a/crates/bevy_ecs/src/schedule.rs b/crates/bevy_ecs/src/schedule.rs
index 0fd2fccc5f..73842f08de 100644
--- a/crates/bevy_ecs/src/schedule.rs
+++ b/crates/bevy_ecs/src/schedule.rs
@@ -2,17 +2,16 @@ use crate::{
     system::{System, ThreadLocalExecution},
     Resources, SystemId, World,
 };
-use rayon::prelude::*;
 use std::{
     borrow::Cow,
-    collections::{HashMap, HashSet},
+    collections::{HashMap, HashSet}, sync::{Mutex, Arc},
 };
 
 #[derive(Default)]
 pub struct Schedule {
-    stages: HashMap<Cow<'static, str>, Vec<Box<dyn System>>>,
-    stage_order: Vec<Cow<'static, str>>,
-    system_ids: HashSet<SystemId>,
+    pub(crate) stages: HashMap<Cow<'static, str>, Vec<Arc<Mutex<Box<dyn System>>>>>,
+    pub(crate) stage_order: Vec<Cow<'static, str>>,
+    pub(crate) system_ids: HashSet<SystemId>,
     is_dirty: bool,
 }
 
@@ -91,7 +90,7 @@ impl Schedule {
             );
         }
         self.system_ids.insert(system.id());
-        systems.push(system);
+        systems.push(Arc::new(Mutex::new(system)));
 
         self.is_dirty = true;
         self
@@ -103,6 +102,7 @@ impl Schedule {
                 for system in stage_systems.iter_mut() {
                     #[cfg(feature = "profiler")]
                     crate::profiler::profiler_start(resources, system.name().clone());
+                    let mut system = system.lock().unwrap();
                     match system.thread_local_execution() {
                         ThreadLocalExecution::NextFlush => system.run(world, resources),
                         ThreadLocalExecution::Immediate => {
@@ -118,6 +118,7 @@ impl Schedule {
                 // "flush"
                 // NOTE: when this is made parallel a full sync is required here
                 for system in stage_systems.iter_mut() {
+                    let mut system = system.lock().unwrap();
                     match system.thread_local_execution() {
                         ThreadLocalExecution::NextFlush => {
                             system.run_thread_local(world, resources)
@@ -129,35 +130,6 @@ impl Schedule {
         }
     }
 
-    pub fn dumb_par_run(&mut self, world: &mut World, resources: &mut Resources) {
-        for stage_name in self.stage_order.iter() {
-            if let Some(stage_systems) = self.stages.get_mut(stage_name) {
-                stage_systems.par_iter_mut().for_each(|system| {
-                    match system.thread_local_execution() {
-                        ThreadLocalExecution::NextFlush => system.run(world, resources),
-                        ThreadLocalExecution::Immediate => {
-                            system.run(world, resources);
-                        }
-                    }
-                });
-
-                // "flush"
-                // NOTE: when this is made parallel a full sync is required here
-                for system in stage_systems.iter_mut() {
-                    match system.thread_local_execution() {
-                        ThreadLocalExecution::NextFlush => {
-                            system.run_thread_local(world, resources)
-                        }
-                        ThreadLocalExecution::Immediate => {
-                            // TODO: this should happen immediately after thread local systems
-                            system.run_thread_local(world, resources)
-                        }
-                    }
-                }
-            }
-        }
-    }
-
     pub fn initialize(&mut self, resources: &mut Resources) {
         if !self.is_dirty {
             return;
@@ -165,32 +137,11 @@ impl Schedule {
 
         for stage in self.stages.values_mut() {
             for system in stage.iter_mut() {
+                let mut system = system.lock().unwrap();
                 system.initialize(resources);
             }
         }
 
         self.is_dirty = false;
     }
-}
-
-// #[cfg(test)]
-// mod tests {
-//     use crate::{Resources, Schedule, World};
-//     use crate::{IntoForEachSystem, IntoQuerySystem};
-
-//     #[test]
-//     fn schedule() {
-//         let mut world = World::new();
-//         let mut resources = Resources::default();
-
-//         world.spawn((1u32, 2u64));
-
-//         let mut schedule = Schedule::default();
-//         schedule.add_stage("A");
-//         schedule.add_stage("B");
-
-//         let xy_system = (|_x: &u32, _y: &mut u64| {
-
-//         }).system();
-//     }
-// }
+}
\ No newline at end of file
diff --git a/crates/bevy_ecs/src/system.rs b/crates/bevy_ecs/src/system.rs
index aa4f15a92d..7965a4c45a 100644
--- a/crates/bevy_ecs/src/system.rs
+++ b/crates/bevy_ecs/src/system.rs
@@ -1,4 +1,4 @@
-use crate::{Resources, World};
+use crate::{Resources, World, executor::ArchetypeAccess};
 use std::borrow::Cow;
 
 #[derive(Copy, Clone)]
@@ -19,6 +19,8 @@ impl SystemId {
 pub trait System: Send + Sync {
     fn name(&self) -> Cow<'static, str>;
     fn id(&self) -> SystemId;
+    fn update_archetype_access(&mut self, world: &World);
+    fn get_archetype_access(&self) -> Option<&ArchetypeAccess>;
     fn thread_local_execution(&self) -> ThreadLocalExecution;
     fn run(&mut self, world: &World, resources: &Resources);
     fn run_thread_local(&mut self, world: &mut World, resources: &mut Resources);