diff --git a/polkadot/Cargo.lock b/polkadot/Cargo.lock
index 3ee8796871..f732d1e1ff 100644
--- a/polkadot/Cargo.lock
+++ b/polkadot/Cargo.lock
@@ -4960,6 +4960,7 @@ dependencies = [
  "polkadot-node-subsystem-util",
  "polkadot-primitives",
  "sp-core",
+ "sp-keystore",
  "thiserror",
  "tracing",
  "tracing-futures",
diff --git a/polkadot/node/core/candidate-selection/Cargo.toml b/polkadot/node/core/candidate-selection/Cargo.toml
index 3d988e21e0..c62cd0b423 100644
--- a/polkadot/node/core/candidate-selection/Cargo.toml
+++ b/polkadot/node/core/candidate-selection/Cargo.toml
@@ -9,6 +9,9 @@ futures = "0.3.8"
 tracing = "0.1.22"
 tracing-futures = "0.2.4"
 thiserror = "1.0.22"
+
+sp-keystore = { git = "https://github.com/paritytech/substrate", branch = "master" }
+
 polkadot-primitives = { path = "../../../primitives" }
 polkadot-node-subsystem = { path = "../../subsystem" }
 polkadot-node-subsystem-util = { path = "../../subsystem-util" }
diff --git a/polkadot/node/core/candidate-selection/src/lib.rs b/polkadot/node/core/candidate-selection/src/lib.rs
index 0eb5242979..5812a47f15 100644
--- a/polkadot/node/core/candidate-selection/src/lib.rs
+++ b/polkadot/node/core/candidate-selection/src/lib.rs
@@ -23,22 +23,28 @@ use futures::{
 	channel::{mpsc, oneshot},
 	prelude::*,
 };
+use sp_keystore::SyncCryptoStorePtr;
 use polkadot_node_subsystem::{
 	errors::ChainApiError,
 	messages::{
 		AllMessages, CandidateBackingMessage, CandidateSelectionMessage, CollatorProtocolMessage,
+		RuntimeApiRequest,
 	},
 };
 use polkadot_node_subsystem_util::{
-	self as util, delegated_subsystem, JobTrait, FromJobCommand, metrics::{self, prometheus},
+	self as util, request_from_runtime, request_validator_groups, delegated_subsystem,
+	JobTrait, FromJobCommand, Validator, metrics::{self, prometheus},
+};
+use polkadot_primitives::v1::{
+	CandidateReceipt, CollatorId, CoreState, CoreIndex, Hash, Id as ParaId, PoV,
 };
-use polkadot_primitives::v1::{CandidateReceipt, CollatorId, Hash, Id as ParaId, PoV};
 use std::pin::Pin;
 use thiserror::Error;
 
 const LOG_TARGET: &'static str = "candidate_selection";
 
 struct CandidateSelectionJob {
+	assignment: ParaId,
 	sender: mpsc::Sender<FromJobCommand>,
 	receiver: mpsc::Receiver<CandidateSelectionMessage>,
 	metrics: Metrics,
@@ -57,30 +63,92 @@ enum Error {
 	ChainApi(#[from] ChainApiError),
 }
 
+macro_rules! try_runtime_api {
+	($x: expr) => {
+		match $x {
+			Ok(x) => x,
+			Err(e) => {
+				tracing::warn!(
+					target: LOG_TARGET,
+					err = ?e,
+					"Failed to fetch runtime API data for job",
+				);
+
+				// We can't do candidate selection work if we don't have the
+				// requisite runtime API data. But these errors should not take
+				// down the node.
+				return Ok(());
+			}
+		}
+	}
+}
+
 impl JobTrait for CandidateSelectionJob {
 	type ToJob = CandidateSelectionMessage;
 	type Error = Error;
-	type RunArgs = ();
+	type RunArgs = SyncCryptoStorePtr;
 	type Metrics = Metrics;
 
 	const NAME: &'static str = "CandidateSelectionJob";
 
-	#[tracing::instrument(skip(_relay_parent, _run_args, metrics, receiver, sender), fields(subsystem = LOG_TARGET))]
+	#[tracing::instrument(skip(keystore, metrics, receiver, sender), fields(subsystem = LOG_TARGET))]
 	fn run(
-		_relay_parent: Hash,
-		_run_args: Self::RunArgs,
+		relay_parent: Hash,
+		keystore: Self::RunArgs,
 		metrics: Self::Metrics,
 		receiver: mpsc::Receiver<CandidateSelectionMessage>,
-		sender: mpsc::Sender<FromJobCommand>,
+		mut sender: mpsc::Sender<FromJobCommand>,
 	) -> Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>> {
 		async move {
-			CandidateSelectionJob::new(metrics, sender, receiver).run_loop().await
+			let (groups, cores) = futures::try_join!(
+				try_runtime_api!(request_validator_groups(relay_parent, &mut sender).await),
+				try_runtime_api!(request_from_runtime(
+					relay_parent,
+					&mut sender,
+					|tx| RuntimeApiRequest::AvailabilityCores(tx),
+				).await),
+			)?;
+
+			let (validator_groups, group_rotation_info) = try_runtime_api!(groups);
+			let cores = try_runtime_api!(cores);
+
+			let n_cores = cores.len();
+
+			let validator = match Validator::new(relay_parent, keystore.clone(), sender.clone()).await {
+				Ok(validator) => validator,
+				Err(util::Error::NotAValidator) => return Ok(()),
+				Err(err) => return Err(Error::Util(err)),
+			};
+
+			let mut assignment = None;
+
+			for (idx, core) in cores.into_iter().enumerate() {
+				// Ignore prospective assignments on occupied cores for the time being.
+				if let CoreState::Scheduled(scheduled) = core {
+					let core_index = CoreIndex(idx as _);
+					let group_index = group_rotation_info.group_for_core(core_index, n_cores);
+					if let Some(g) = validator_groups.get(group_index.0 as usize) {
+						if g.contains(&validator.index()) {
+							assignment = Some(scheduled.para_id);
+							break;
+						}
+					}
+				}
+			}
+
+			let assignment = match assignment {
+				Some(assignment) => assignment,
+				None => return Ok(()),
+			};
+
+			CandidateSelectionJob::new(assignment, metrics, sender, receiver).run_loop().await
 		}.boxed()
 	}
 }
 
 impl CandidateSelectionJob {
 	pub fn new(
+		assignment: ParaId,
 		metrics: Metrics,
 		sender: mpsc::Sender<FromJobCommand>,
 		receiver: mpsc::Receiver<CandidateSelectionMessage>,
@@ -89,6 +157,7 @@ impl CandidateSelectionJob {
 			sender,
 			receiver,
 			metrics,
+			assignment,
 			seconded_candidate: None,
 		}
 	}
@@ -128,6 +197,23 @@ impl CandidateSelectionJob {
 	) {
 		let _timer = self.metrics.time_handle_collation();
 
+		if self.assignment != para_id {
+			tracing::info!(
+				target: LOG_TARGET,
+				"Collator {:?} sent a collation outside of our assignment {:?}",
+				collator_id,
+				para_id,
+			);
+			if let Err(err) = forward_invalidity_note(&collator_id, &mut self.sender).await {
+				tracing::warn!(
+					target: LOG_TARGET,
+					err = ?err,
+					"failed to forward invalidity note",
+				);
+			}
+			return;
+		}
+
 		if self.seconded_candidate.is_none() {
 			let (candidate_receipt, pov) =
 				match get_collation(
@@ -342,7 +428,7 @@ impl metrics::Metrics for Metrics {
 	}
 }
 
-delegated_subsystem!(CandidateSelectionJob((), Metrics) <- CandidateSelectionMessage as CandidateSelectionSubsystem);
+delegated_subsystem!(CandidateSelectionJob(SyncCryptoStorePtr, Metrics) <- CandidateSelectionMessage as CandidateSelectionSubsystem);
 
 #[cfg(test)]
 mod tests {
@@ -365,6 +451,7 @@ mod tests {
 		let (to_job_tx, to_job_rx) = mpsc::channel(0);
 		let (from_job_tx, from_job_rx) = mpsc::channel(0);
 		let mut job = CandidateSelectionJob {
+			assignment: 123.into(),
 			sender: from_job_tx,
 			receiver: to_job_rx,
 			metrics: Default::default(),
diff --git a/polkadot/node/service/src/lib.rs b/polkadot/node/service/src/lib.rs
index e59994cdcc..c9f654ea22 100644
--- a/polkadot/node/service/src/lib.rs
+++ b/polkadot/node/service/src/lib.rs
@@ -367,7 +367,7 @@ where
 		),
 		candidate_selection: CandidateSelectionSubsystem::new(
 			spawner.clone(),
-			(),
+			keystore.clone(),
 			Metrics::register(registry)?,
 		),
 		candidate_validation: CandidateValidationSubsystem::new(