diff --git a/Cargo.lock b/Cargo.lock
index d7b1350c1f529..cfcf5573c0bff 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -511,10 +511,12 @@ dependencies = [
 name = "beefy-merkle-tree"
 version = "4.0.0-dev"
 dependencies = [
+ "beefy-primitives",
  "env_logger 0.9.0",
  "hex",
  "hex-literal",
  "log",
+ "sp-api",
  "tiny-keccak",
 ]
 
@@ -10646,6 +10648,7 @@ dependencies = [
 name = "substrate-test-runtime"
 version = "2.0.0"
 dependencies = [
+ "beefy-merkle-tree",
  "beefy-primitives",
  "cfg-if 1.0.0",
  "frame-support",
diff --git a/frame/beefy-mmr/primitives/Cargo.toml b/frame/beefy-mmr/primitives/Cargo.toml
index 7878dc3d22837..f30a418def042 100644
--- a/frame/beefy-mmr/primitives/Cargo.toml
+++ b/frame/beefy-mmr/primitives/Cargo.toml
@@ -13,6 +13,9 @@ hex = { version = "0.4", default-features = false, optional = true }
 log = { version = "0.4", default-features = false, optional = true }
 tiny-keccak = { version = "2.0.2", features = ["keccak"], optional = true }
 
+beefy-primitives = { version = "4.0.0-dev", default-features = false, path = "../../../primitives/beefy" }
+sp-api = { version = "4.0.0-dev", default-features = false, path = "../../../primitives/api" }
+
 [dev-dependencies]
 env_logger = "0.9"
 hex = "0.4"
@@ -22,4 +25,7 @@ hex-literal = "0.3"
 debug = ["hex", "hex/std", "log"]
 default = ["debug", "keccak", "std"]
 keccak = ["tiny-keccak"]
-std = []
+std = [
+	"beefy-primitives/std",
+	"sp-api/std"
+]
diff --git a/frame/beefy-mmr/primitives/src/lib.rs b/frame/beefy-mmr/primitives/src/lib.rs
index 04fa11760765b..664fd18199dd0 100644
--- a/frame/beefy-mmr/primitives/src/lib.rs
+++ b/frame/beefy-mmr/primitives/src/lib.rs
@@ -36,6 +36,8 @@ extern crate alloc;
 #[cfg(not(feature = "std"))]
 use alloc::vec::Vec;
 
+use beefy_primitives::mmr::{BeefyAuthoritySet, BeefyNextAuthoritySet};
+
 /// Supported hashing output size.
 ///
 /// The size is restricted to 32 bytes to allow for a more optimised implementation.
@@ -375,6 +377,21 @@ where
 	}
 }
 
+sp_api::decl_runtime_apis! {
+	/// API useful for BEEFY light clients.
+	pub trait BeefyMmrApi<H>
+	where
+		H: From<Hash> + Into<Hash>,
+		BeefyAuthoritySet<H>: sp_api::Decode,
+	{
+		/// Return the currently active BEEFY authority set proof.
+		fn authority_set_proof() -> BeefyAuthoritySet<H>;
+
+		/// Return the next/queued BEEFY authority set proof.
+		fn next_authority_set_proof() -> BeefyNextAuthoritySet<H>;
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;
diff --git a/frame/beefy-mmr/src/lib.rs b/frame/beefy-mmr/src/lib.rs
index 8b904d6aefd5f..456d6e77aa8eb 100644
--- a/frame/beefy-mmr/src/lib.rs
+++ b/frame/beefy-mmr/src/lib.rs
@@ -36,7 +36,10 @@
 use sp_runtime::traits::{Convert, Hash, Member};
 use sp_std::prelude::*;
 
-use beefy_primitives::mmr::{BeefyDataProvider, BeefyNextAuthoritySet, MmrLeaf, MmrLeafVersion};
+use beefy_primitives::{
+	mmr::{BeefyAuthoritySet, BeefyDataProvider, BeefyNextAuthoritySet, MmrLeaf, MmrLeafVersion},
+	ValidatorSet as BeefyValidatorSet,
+};
 use pallet_mmr::{LeafDataProvider, ParentNumberAndHash};
 
 use frame_support::{crypto::ecdsa::ECDSAExt, traits::Get};
@@ -124,6 +127,12 @@ pub mod pallet {
 		type BeefyDataProvider: BeefyDataProvider<Self::LeafExtra>;
 	}
 
+	/// Details of current BEEFY authority set.
+	#[pallet::storage]
+	#[pallet::getter(fn beefy_authorities)]
+	pub type BeefyAuthorities<T: Config> =
+		StorageValue<_, BeefyAuthoritySet<MerkleRootOf<T>>, ValueQuery>;
+
 	/// Details of next BEEFY authority set.
 	///
 	/// This storage entry is used as cache for calls to `update_beefy_next_authority_set`.
@@ -149,7 +158,7 @@ where
 			version: T::LeafVersion::get(),
 			parent_number_and_hash: ParentNumberAndHash::<T>::leaf_data(),
 			leaf_extra: T::BeefyDataProvider::extra_data(),
-			beefy_next_authority_set: Pallet::<T>::update_beefy_next_authority_set(),
+			beefy_next_authority_set: Pallet::<T>::beefy_next_authorities(),
 		}
 	}
 }
@@ -163,35 +172,55 @@ where
 	}
 }
 
+impl<T> beefy_primitives::OnNewValidatorSet<<T as pallet_beefy::Config>::BeefyId> for Pallet<T>
+where
+	T: pallet::Config,
+	MerkleRootOf<T>: From<beefy_merkle_tree::Hash> + Into<beefy_merkle_tree::Hash>,
+{
+	/// Compute and cache BEEFY authority sets based on updated BEEFY validator sets.
+	fn on_new_validator_set(
+		current_set: &BeefyValidatorSet<<T as pallet_beefy::Config>::BeefyId>,
+		next_set: &BeefyValidatorSet<<T as pallet_beefy::Config>::BeefyId>,
+	) {
+		let current = Pallet::<T>::compute_authority_set(current_set);
+		let next = Pallet::<T>::compute_authority_set(next_set);
+		// cache the result
+		BeefyAuthorities::<T>::put(&current);
+		BeefyNextAuthorities::<T>::put(&next);
+	}
+}
+
 impl<T: Config> Pallet<T>
 where
 	MerkleRootOf<T>: From<beefy_merkle_tree::Hash> + Into<beefy_merkle_tree::Hash>,
 {
-	/// Returns details of the next BEEFY authority set.
+	/// Return the currently active BEEFY authority set proof.
+	pub fn authority_set_proof() -> BeefyAuthoritySet<MerkleRootOf<T>> {
+		Pallet::<T>::beefy_authorities()
+	}
+
+	/// Return the next/queued BEEFY authority set proof.
+	pub fn next_authority_set_proof() -> BeefyNextAuthoritySet<MerkleRootOf<T>> {
+		Pallet::<T>::beefy_next_authorities()
+	}
+
+	/// Returns details of a BEEFY authority set.
 	///
 	/// Details contain authority set id, authority set length and a merkle root,
 	/// constructed from uncompressed secp256k1 public keys converted to Ethereum addresses
 	/// of the next BEEFY authority set.
-	///
-	/// This function will use a storage-cached entry in case the set didn't change, or compute and
-	/// cache new one in case it did.
-	fn update_beefy_next_authority_set() -> BeefyNextAuthoritySet<MerkleRootOf<T>> {
-		let id = pallet_beefy::Pallet::<T>::validator_set_id() + 1;
-		let current_next = Self::beefy_next_authorities();
-		// avoid computing the merkle tree if validator set id didn't change.
-		if id == current_next.id {
-			return current_next
-		}
-
-		let beefy_addresses = pallet_beefy::Pallet::<T>::next_authorities()
+	fn compute_authority_set(
+		validator_set: &BeefyValidatorSet<<T as pallet_beefy::Config>::BeefyId>,
+	) -> BeefyAuthoritySet<MerkleRootOf<T>> {
+		let id = validator_set.id();
+		let beefy_addresses = validator_set
+			.validators()
 			.into_iter()
+			.cloned()
 			.map(T::BeefyAuthorityToMerkleLeaf::convert)
 			.collect::<Vec<_>>();
 		let len = beefy_addresses.len() as u32;
 		let root = beefy_merkle_tree::merkle_root::<Self, _, _>(beefy_addresses).into();
-		let next_set = BeefyNextAuthoritySet { id, len, root };
-		// cache the result
-		BeefyNextAuthorities::<T>::put(&next_set);
-		next_set
+		BeefyAuthoritySet { id, len, root }
 	}
 }
diff --git a/frame/beefy-mmr/src/mock.rs b/frame/beefy-mmr/src/mock.rs
index c9dbdb3b2e16a..8a673c9d4e914 100644
--- a/frame/beefy-mmr/src/mock.rs
+++ b/frame/beefy-mmr/src/mock.rs
@@ -125,6 +125,7 @@ impl pallet_mmr::Config for Test {
 impl pallet_beefy::Config for Test {
 	type BeefyId = BeefyId;
 	type MaxAuthorities = ConstU32<100>;
+	type OnNewValidatorSet = BeefyMmr;
 }
 
 parameter_types! {
diff --git a/frame/beefy-mmr/src/tests.rs b/frame/beefy-mmr/src/tests.rs
index fd3ecd5067155..d9cd8c8a5d8c8 100644
--- a/frame/beefy-mmr/src/tests.rs
+++ b/frame/beefy-mmr/src/tests.rs
@@ -149,3 +149,53 @@ fn should_contain_valid_leaf_data() {
 		}
 	);
 }
+
+#[test]
+fn should_update_authorities() {
+	new_test_ext(vec![1, 2, 3, 4]).execute_with(|| {
+		let auth_set = BeefyMmr::authority_set_proof();
+		let next_auth_set = BeefyMmr::next_authority_set_proof();
+
+		// check current authority set
+		assert_eq!(0, auth_set.id);
+		assert_eq!(2, auth_set.len);
+		let want: H256 =
+			hex!("176e73f1bf656478b728e28dd1a7733c98621b8acf830bff585949763dca7a96").into();
+		assert_eq!(want, auth_set.root);
+
+		// next authority set should have same validators but different id
+		assert_eq!(1, next_auth_set.id);
+		assert_eq!(auth_set.len, next_auth_set.len);
+		assert_eq!(auth_set.root, next_auth_set.root);
+
+		let announced_set = next_auth_set;
+		init_block(1);
+		let auth_set = BeefyMmr::authority_set_proof();
+		let next_auth_set = BeefyMmr::next_authority_set_proof();
+
+		// check new auth are expected ones
+		assert_eq!(announced_set, auth_set);
+		assert_eq!(1, auth_set.id);
+		// check next auth set
+		assert_eq!(2, next_auth_set.id);
+		let want: H256 =
+			hex!("9c6b2c1b0d0b25a008e6c882cc7b415f309965c72ad2b944ac0931048ca31cd5").into();
+		assert_eq!(2, next_auth_set.len);
+		assert_eq!(want, next_auth_set.root);
+
+		let announced_set = next_auth_set;
+		init_block(2);
+		let auth_set = BeefyMmr::authority_set_proof();
+		let next_auth_set = BeefyMmr::next_authority_set_proof();
+
+		// check new auth are expected ones
+		assert_eq!(announced_set, auth_set);
+		assert_eq!(2, auth_set.id);
+		// check next auth set
+		assert_eq!(3, next_auth_set.id);
+		let want: H256 =
+			hex!("9c6b2c1b0d0b25a008e6c882cc7b415f309965c72ad2b944ac0931048ca31cd5").into();
+		assert_eq!(2, next_auth_set.len);
+		assert_eq!(want, next_auth_set.root);
+	});
+}
diff --git a/frame/beefy/src/lib.rs b/frame/beefy/src/lib.rs
index a0cba2270b37d..fce531d3f5dd7 100644
--- a/frame/beefy/src/lib.rs
+++ b/frame/beefy/src/lib.rs
@@ -32,7 +32,9 @@ use sp_runtime::{
 };
 use sp_std::prelude::*;
 
-use beefy_primitives::{AuthorityIndex, ConsensusLog, ValidatorSet, BEEFY_ENGINE_ID};
+use beefy_primitives::{
+	AuthorityIndex, ConsensusLog, OnNewValidatorSet, ValidatorSet, BEEFY_ENGINE_ID,
+};
 
 #[cfg(test)]
 mod mock;
@@ -58,6 +60,13 @@ pub mod pallet {
 
 		/// The maximum number of authorities that can be added.
 		type MaxAuthorities: Get<u32>;
+
+		/// A hook to act on the new BEEFY validator set.
+		///
+		/// For some applications it might be beneficial to make the BEEFY validator set available
+		/// externally apart from having it in the storage. For instance you might cache a light
+		/// weight MMR root over validators and make it available for Light Clients.
+		type OnNewValidatorSet: OnNewValidatorSet<<Self as Config>::BeefyId>;
 	}
 
 	#[pallet::pallet]
@@ -118,20 +127,29 @@ impl<T: Config> Pallet<T> {
 	) {
 		<Authorities<T>>::put(&new);
 
-		let next_id = Self::validator_set_id() + 1u64;
-		<ValidatorSetId<T>>::put(next_id);
-		if let Some(validator_set) = ValidatorSet::<T::BeefyId>::new(new, next_id) {
+		let new_id = Self::validator_set_id() + 1u64;
+		<ValidatorSetId<T>>::put(new_id);
+
+		<NextAuthorities<T>>::put(&queued);
+
+		if let Some(validator_set) = ValidatorSet::<T::BeefyId>::new(new, new_id) {
 			let log = DigestItem::Consensus(
 				BEEFY_ENGINE_ID,
-				ConsensusLog::AuthoritiesChange(validator_set).encode(),
+				ConsensusLog::AuthoritiesChange(validator_set.clone()).encode(),
 			);
 			<frame_system::Pallet<T>>::deposit_log(log);
-		}
 
-		<NextAuthorities<T>>::put(&queued);
+			let next_id = new_id + 1;
+			if let Some(next_validator_set) = ValidatorSet::<T::BeefyId>::new(queued, next_id) {
+				<T::OnNewValidatorSet as OnNewValidatorSet<_>>::on_new_validator_set(
+					&validator_set,
+					&next_validator_set,
+				);
+			}
+		}
 	}
 
-	fn initialize_authorities(authorities: &[T::BeefyId]) -> Result<(), ()> {
+	fn initialize_authorities(authorities: &Vec<T::BeefyId>) -> Result<(), ()> {
 		if authorities.is_empty() {
 			return Ok(())
 		}
@@ -141,12 +159,25 @@ impl<T: Config> Pallet<T> {
 		}
 
 		let bounded_authorities =
-			BoundedSlice::<T::BeefyId, T::MaxAuthorities>::try_from(authorities)?;
+			BoundedSlice::<T::BeefyId, T::MaxAuthorities>::try_from(authorities.as_slice())?;
 
+		let id = 0;
 		<Authorities<T>>::put(bounded_authorities);
-		<ValidatorSetId<T>>::put(0);
+		<ValidatorSetId<T>>::put(id);
 		// Like `pallet_session`, initialize the next validator set as well.
 		<NextAuthorities<T>>::put(bounded_authorities);
+
+		if let Some(validator_set) = ValidatorSet::<T::BeefyId>::new(authorities.clone(), id) {
+			let next_id = id + 1;
+			if let Some(next_validator_set) =
+				ValidatorSet::<T::BeefyId>::new(authorities.clone(), next_id)
+			{
+				<T::OnNewValidatorSet as OnNewValidatorSet<_>>::on_new_validator_set(
+					&validator_set,
+					&next_validator_set,
+				);
+			}
+		}
 		Ok(())
 	}
 }
diff --git a/frame/beefy/src/mock.rs b/frame/beefy/src/mock.rs
index 27796b5b2206c..3bb59c7c39485 100644
--- a/frame/beefy/src/mock.rs
+++ b/frame/beefy/src/mock.rs
@@ -87,6 +87,7 @@ impl frame_system::Config for Test {
 impl pallet_beefy::Config for Test {
 	type BeefyId = BeefyId;
 	type MaxAuthorities = ConstU32<100>;
+	type OnNewValidatorSet = ();
 }
 
 parameter_types! {
diff --git a/primitives/beefy/src/lib.rs b/primitives/beefy/src/lib.rs
index 8dbdd66f3559b..87f1b8756af65 100644
--- a/primitives/beefy/src/lib.rs
+++ b/primitives/beefy/src/lib.rs
@@ -154,6 +154,20 @@ pub struct VoteMessage<Number, Id, Signature> {
 	pub signature: Signature,
 }
 
+/// New BEEFY validator set notification hook.
+pub trait OnNewValidatorSet<AuthorityId> {
+	/// Function called by the pallet when BEEFY validator set changes.
+	fn on_new_validator_set(
+		validator_set: &ValidatorSet<AuthorityId>,
+		next_validator_set: &ValidatorSet<AuthorityId>,
+	);
+}
+
+/// No-op implementation of [OnNewValidatorSet].
+impl<AuthorityId> OnNewValidatorSet<AuthorityId> for () {
+	fn on_new_validator_set(_: &ValidatorSet<AuthorityId>, _: &ValidatorSet<AuthorityId>) {}
+}
+
 sp_api::decl_runtime_apis! {
 	/// API necessary for BEEFY voters.
 	pub trait BeefyApi
diff --git a/primitives/beefy/src/mmr.rs b/primitives/beefy/src/mmr.rs
index 426a1ba5ff80b..761eee9f8ef85 100644
--- a/primitives/beefy/src/mmr.rs
+++ b/primitives/beefy/src/mmr.rs
@@ -95,10 +95,10 @@ impl MmrLeafVersion {
 	}
 }
 
-/// Details of the next BEEFY authority set.
+/// Details of a BEEFY authority set.
 #[derive(Debug, Default, PartialEq, Eq, Clone, Encode, Decode, TypeInfo, MaxEncodedLen)]
-pub struct BeefyNextAuthoritySet<MerkleRoot> {
-	/// Id of the next set.
+pub struct BeefyAuthoritySet<MerkleRoot> {
+	/// Id of the set.
 	///
 	/// Id is required to correlate BEEFY signed commitments with the validator set.
 	/// Light Client can easily verify that the commitment witness it is getting is
@@ -106,11 +106,11 @@ pub struct BeefyNextAuthoritySet<MerkleRoot> {
 	pub id: crate::ValidatorSetId,
 	/// Number of validators in the set.
 	///
-	/// Some BEEFY Light Clients may use an interactive protocol to verify only subset
+	/// Some BEEFY Light Clients may use an interactive protocol to verify only a subset
 	/// of signatures. We put set length here, so that these clients can verify the minimal
 	/// number of required signatures.
 	pub len: u32,
-	/// Merkle Root Hash build from BEEFY AuthorityIds.
+	/// Merkle Root Hash built from BEEFY AuthorityIds.
 	///
 	/// This is used by Light Clients to confirm that the commitments are signed by the correct
 	/// validator set. Light Clients using interactive protocol, might verify only subset of
@@ -118,6 +118,9 @@ pub struct BeefyNextAuthoritySet<MerkleRoot> {
 	pub root: MerkleRoot,
 }
 
+/// Details of the next BEEFY authority set.
+pub type BeefyNextAuthoritySet<MerkleRoot> = BeefyAuthoritySet<MerkleRoot>;
+
 #[cfg(test)]
 mod tests {
 	use super::*;
diff --git a/test-utils/runtime/Cargo.toml b/test-utils/runtime/Cargo.toml
index 739be9ec8bdd8..1c2707b3719ad 100644
--- a/test-utils/runtime/Cargo.toml
+++ b/test-utils/runtime/Cargo.toml
@@ -14,6 +14,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 
 [dependencies]
 beefy-primitives = { version = "4.0.0-dev", default-features = false, path = "../../primitives/beefy" }
+beefy-merkle-tree = { version = "4.0.0-dev", default-features = false, path = "../../frame/beefy-mmr/primitives" }
 sp-application-crypto = { version = "6.0.0", default-features = false, path = "../../primitives/application-crypto" }
 sp-consensus-aura = { version = "0.10.0-dev", default-features = false, path = "../../primitives/consensus/aura" }
 sp-consensus-babe = { version = "0.10.0-dev", default-features = false, path = "../../primitives/consensus/babe" }
@@ -67,6 +68,7 @@ default = [
 ]
 std = [
 	"beefy-primitives/std",
+	"beefy-merkle-tree/std",
 	"sp-application-crypto/std",
 	"sp-consensus-aura/std",
 	"sp-consensus-babe/std",
diff --git a/test-utils/runtime/src/lib.rs b/test-utils/runtime/src/lib.rs
index 555f29e5991f7..ea62f2ac84f3d 100644
--- a/test-utils/runtime/src/lib.rs
+++ b/test-utils/runtime/src/lib.rs
@@ -947,6 +947,16 @@ cfg_if! {
 				}
 			}
 
+			impl beefy_merkle_tree::BeefyMmrApi<Block, beefy_primitives::MmrRootHash> for RuntimeApi {
+				fn authority_set_proof() -> beefy_primitives::mmr::BeefyAuthoritySet<beefy_primitives::MmrRootHash> {
+					Default::default()
+				}
+
+				fn next_authority_set_proof() -> beefy_primitives::mmr::BeefyNextAuthoritySet<beefy_primitives::MmrRootHash> {
+					Default::default()
+				}
+			}
+
 			impl frame_system_rpc_runtime_api::AccountNonceApi<Block, AccountId, Index> for Runtime {
 				fn account_nonce(_account: AccountId) -> Index {
 					0