diff --git a/lib/lambda_ethereum_consensus/p2p/gossip/attestation.ex b/lib/lambda_ethereum_consensus/p2p/gossip/attestation.ex
index 223db2c07..110dd57f0 100644
--- a/lib/lambda_ethereum_consensus/p2p/gossip/attestation.ex
+++ b/lib/lambda_ethereum_consensus/p2p/gossip/attestation.ex
@@ -67,20 +67,29 @@ defmodule LambdaEthereumConsensus.P2P.Gossip.Attestation do
     Libp2pPort.publish(topic, message)
   end
 
+  @spec subscribe(non_neg_integer()) :: :ok
+  def subscribe(subnet_id),
+    do: Libp2pPort.async_subscribe_to_topic(topic(subnet_id), __MODULE__)
+
   @spec collect(non_neg_integer(), Types.Attestation.t()) :: :ok
   def collect(subnet_id, attestation) do
     join(subnet_id)
     AttSubnetInfo.new_subnet_with_attestation(subnet_id, attestation)
-    Libp2pPort.async_subscribe_to_topic(topic(subnet_id), __MODULE__)
+    subscribe(subnet_id)
   end
 
-  @spec stop_collecting(non_neg_integer()) ::
-          {:ok, list(Types.Attestation.t())} | {:error, String.t()}
-  def stop_collecting(subnet_id) do
+  @spec unsubscribe(non_neg_integer()) :: :ok
+  def unsubscribe(subnet_id) do
     # TODO: (#1289) implement some way to unsubscribe without leaving the topic
     topic = topic(subnet_id)
     Libp2pPort.leave_topic(topic)
     Libp2pPort.join_topic(topic)
+  end
+
+  @spec stop_collecting(non_neg_integer()) ::
+          {:ok, list(Types.Attestation.t())} | {:error, String.t()}
+  def stop_collecting(subnet_id) do
+    unsubscribe(subnet_id)
     AttSubnetInfo.stop_collecting(subnet_id)
   end
 
diff --git a/lib/lambda_ethereum_consensus/p2p/gossip/sync_committee.ex b/lib/lambda_ethereum_consensus/p2p/gossip/sync_committee.ex
index 5e6e5c15b..fb5ff6fba 100644
--- a/lib/lambda_ethereum_consensus/p2p/gossip/sync_committee.ex
+++ b/lib/lambda_ethereum_consensus/p2p/gossip/sync_committee.ex
@@ -72,25 +72,34 @@ defmodule LambdaEthereumConsensus.P2P.Gossip.SyncCommittee do
     Libp2pPort.publish(topic, message)
   end
 
+  @spec subscribe(non_neg_integer()) :: :ok
+  def subscribe(subnet_id),
+    do: Libp2pPort.async_subscribe_to_topic(topic(subnet_id), __MODULE__)
+
   @spec collect([non_neg_integer()], Types.SyncCommitteeMessage.t()) :: :ok
   def collect(subnet_ids, message) do
     join(subnet_ids)
 
     for subnet_id <- subnet_ids do
       SyncSubnetInfo.new_subnet_with_message(subnet_id, message)
-      Libp2pPort.async_subscribe_to_topic(topic(subnet_id), __MODULE__)
+      subscribe(subnet_id)
     end
 
     :ok
   end
 
-  @spec stop_collecting(non_neg_integer()) ::
-          {:ok, list(Types.SyncCommitteeMessage.t())} | {:error, String.t()}
-  def stop_collecting(subnet_id) do
+  @spec unsubscribe(non_neg_integer()) :: :ok
+  def unsubscribe(subnet_id) do
     # TODO: (#1289) implement some way to unsubscribe without leaving the topic
     topic = topic(subnet_id)
     Libp2pPort.leave_topic(topic)
     Libp2pPort.join_topic(topic)
+  end
+
+  @spec stop_collecting(non_neg_integer()) ::
+          {:ok, list(Types.SyncCommitteeMessage.t())} | {:error, String.t()}
+  def stop_collecting(subnet_id) do
+    unsubscribe(subnet_id)
     SyncSubnetInfo.stop_collecting(subnet_id)
   end
 
diff --git a/lib/lambda_ethereum_consensus/validator/duties.ex b/lib/lambda_ethereum_consensus/validator/duties.ex
index 8867ccf97..9b0d3ec3a 100644
--- a/lib/lambda_ethereum_consensus/validator/duties.ex
+++ b/lib/lambda_ethereum_consensus/validator/duties.ex
@@ -41,8 +41,17 @@ defmodule LambdaEthereumConsensus.Validator.Duties do
           aggregation: [sync_committee_aggregator_duty()]
         }
 
+  @typedoc "Set of subnet indices for a particular slot, used in attestations and sync committees."
+  @type subnets :: MapSet.t(subnet_index :: Types.uint64())
+
   @typedoc "Useful precalculated data not tied to a particular slot/duty."
-  @type shared_data_for_duties :: %{sync_subcommittee_participants: %{}}
+  @type shared_data_for_duties :: %{
+          subnets: %{
+            attesters: %{Types.slot() => subnets},
+            sync_committees: %{Types.slot() => subnets}
+          },
+          sync_subcommittee_participants: %{}
+        }
 
   @type attester_duties :: [attester_duty()]
   @type proposer_duties :: [proposer_duty()]
@@ -103,11 +112,20 @@ defmodule LambdaEthereumConsensus.Validator.Duties do
               |> then(&{&1, compute_sync_subcommittee_participants(beacon, epoch)})
           end
 
+        new_subnets_for_attestations = compute_subnets_for_attestations(new_attesters)
+        new_subnets_for_sync_committees = compute_subnets_for_sync_committees(new_sync_committees)
+
         new_duties = %{
           proposers: new_proposers,
           attesters: new_attesters,
           sync_committees: new_sync_committees,
-          shared: %{sync_subcommittee_participants: sync_subcommittee_participants}
+          shared: %{
+            subnets: %{
+              attesters: new_subnets_for_attestations,
+              sync_committees: new_subnets_for_sync_committees
+            },
+            sync_subcommittee_participants: sync_subcommittee_participants
+          }
         }
 
         log_duties_for_epoch(new_duties, epoch)
@@ -312,6 +330,25 @@ defmodule LambdaEthereumConsensus.Validator.Duties do
     Map.put(duty, :subnet_id, subnet_id)
   end
 
+  defp compute_subnets_for_attestations(attester_duties) do
+    for {slot, duties} <- attester_duties,
+        %{should_aggregate?: true, committee_index: subnet_id} <- duties,
+        reduce: %{} do
+      acc ->
+        Map.update(acc, slot, MapSet.new([subnet_id]), &MapSet.put(&1, subnet_id))
+    end
+  end
+
+  defp compute_subnets_for_sync_committees(sync_committee_duties) do
+    for {slot, duties} <- sync_committee_duties,
+        %{aggregation: agg} when agg != [] <- duties,
+        %{subcommittee_index: subnet_id} <- agg,
+        reduce: %{} do
+      acc ->
+        Map.update(acc, slot, MapSet.new([subnet_id]), &MapSet.put(&1, subnet_id))
+    end
+  end
+
   ############################
   # Accessors
 
@@ -350,6 +387,17 @@ defmodule LambdaEthereumConsensus.Validator.Duties do
     end
   end
 
+  @spec current_subnets(duties(), Types.epoch(), Types.slot()) ::
+          %{attesters: subnets, sync_committees: subnets}
+  def current_subnets(duties, epoch, slot) do
+    %{
+      attesters: get_in(duties, [epoch, :shared, :subnets, :attesters, slot]) || MapSet.new(),
+      sync_committees:
+        get_in(duties, [epoch, :shared, :subnets, :sync_committees, max(0, slot - 1)]) ||
+          MapSet.new()
+    }
+  end
+
   @spec sync_subcommittee_participants(duties(), Types.epoch()) :: %{
           non_neg_integer() => [non_neg_integer()]
         }
@@ -399,23 +447,41 @@ defmodule LambdaEthereumConsensus.Validator.Duties do
 
   @spec log_duties_for_epoch(duties(), Types.epoch()) :: :ok
   def log_duties_for_epoch(
-        %{proposers: proposers, attesters: attesters, sync_committees: sync_committees},
+        %{
+          proposers: proposers,
+          attesters: attesters,
+          sync_committees: sync_committees,
+          shared: shared
+        },
         epoch
       ) do
     Logger.info(
       "[Duties] Proposers for epoch #{epoch} (slot=>validator):\n #{inspect(proposers)}"
     )
 
-    for %{
-          subnet_ids: si,
-          validator_index: vi,
-          aggregation: agg
-        } <- sync_committees do
-      Logger.info(
-        "[Duties] Sync committee for epoch: #{epoch}, validator_index: #{vi} will broadcast on subnet_ids: #{inspect(si)}.\n Slots: #{inspect(agg |> Map.keys() |> Enum.join(", "))}"
-      )
+    Logger.debug(
+      "[Duties] SyncCommittees Subnets for epoch #{epoch}: #{inspect(shared.subnets.sync_committees)}"
+    )
+
+    for {slot, sync_duties} <- sync_committees,
+        length(sync_duties) > 0 do
+      Logger.debug("[Duties] Sync committee for epoch: #{epoch}, slot: #{slot}:")
+
+      for %{
+            validator_index: vi,
+            subnet_ids: si,
+            aggregation: agg
+          } <- sync_duties do
+        Logger.debug(
+          "[Duties] Validator: #{vi}, will broadcast in subnets: #{si} and aggregate in #{inspect(agg |> Enum.map(& &1.subcommittee_index))}."
+        )
+      end
     end
 
+    Logger.debug(
+      "[Duties] Attesters Subnets for epoch #{epoch}: #{inspect(shared.subnets.attesters)}"
+    )
+
     for {slot, att_duties} <- attesters,
         length(att_duties) > 0 do
       Logger.debug("[Duties] Attesters for epoch: #{epoch}, slot #{slot}:")
diff --git a/lib/lambda_ethereum_consensus/validator/validator_set.ex b/lib/lambda_ethereum_consensus/validator/validator_set.ex
index 5ae727e35..05f420928 100644
--- a/lib/lambda_ethereum_consensus/validator/validator_set.ex
+++ b/lib/lambda_ethereum_consensus/validator/validator_set.ex
@@ -5,10 +5,16 @@ defmodule LambdaEthereumConsensus.ValidatorSet do
   simplify the delegation of work.
   """
 
-  defstruct slot: nil, head_root: nil, duties: %{}, validators: %{}
+  defstruct slot: nil,
+            head_root: nil,
+            duties: %{},
+            subscribed_subnets: %{attesters: MapSet.new(), sync_committees: MapSet.new()},
+            validators: %{}
 
   require Logger
 
+  alias LambdaEthereumConsensus.P2P.Gossip.Attestation
+  alias LambdaEthereumConsensus.P2P.Gossip.SyncCommittee
   alias LambdaEthereumConsensus.StateTransition
   alias LambdaEthereumConsensus.StateTransition.Misc
   alias LambdaEthereumConsensus.Store.CheckpointStates
@@ -21,6 +27,7 @@ defmodule LambdaEthereumConsensus.ValidatorSet do
           slot: Types.slot(),
           head_root: Types.root() | nil,
           duties: %{Types.epoch() => Duties.duties()},
+          subscribed_subnets: %{attesters: Duties.subnets(), sync_committees: Duties.subnets()},
           validators: validators()
         }
 
@@ -137,7 +144,9 @@ defmodule LambdaEthereumConsensus.ValidatorSet do
   end
 
   defp process_tick(%{head_root: head_root} = set, epoch, {slot, :first_third}) do
-    maybe_propose(set, epoch, slot, head_root)
+    set
+    |> maybe_resubscribe_to_subnets(epoch, slot)
+    |> maybe_propose(epoch, slot, head_root)
   end
 
   defp process_tick(%{head_root: head_root} = set, epoch, {slot, :second_third}) do
@@ -325,6 +334,30 @@ defmodule LambdaEthereumConsensus.ValidatorSet do
     |> then(&%{set | duties: &1})
   end
 
+  ##########################
+  # Subnets
+
+  defp maybe_resubscribe_to_subnets(set, epoch, slot) do
+    %{subscribed_subnets: %{attesters: old_att_subnets, sync_committees: old_sync_subnets}} = set
+
+    %{attesters: new_att_subnets, sync_committees: new_sync_subnets} =
+      Duties.current_subnets(set.duties, epoch, slot)
+
+    unsubscribe_att = MapSet.difference(old_att_subnets, new_att_subnets)
+    unsubscribe_sync = MapSet.difference(old_sync_subnets, new_sync_subnets)
+
+    Enum.each(unsubscribe_att, &Attestation.unsubscribe/1)
+    Enum.each(unsubscribe_sync, &SyncCommittee.unsubscribe/1)
+
+    subscribe_att = MapSet.difference(new_att_subnets, old_att_subnets)
+    subscribe_sync = MapSet.difference(new_sync_subnets, old_sync_subnets)
+
+    Enum.each(subscribe_att, &Attestation.subscribe/1)
+    Enum.each(subscribe_sync, &SyncCommittee.subscribe/1)
+
+    %{set | subscribed_subnets: %{attesters: new_att_subnets, sync_committees: new_sync_subnets}}
+  end
+
   ##########################
   # Target State
   # TODO: (#1278) This should be taken from the store as noted by arkenan.
diff --git a/lib/types/att_subnet_info.ex b/lib/types/att_subnet_info.ex
index 6f0c2594b..b909e8e8e 100644
--- a/lib/types/att_subnet_info.ex
+++ b/lib/types/att_subnet_info.ex
@@ -44,13 +44,13 @@ defmodule Types.AttSubnetInfo do
 
   @doc """
   Adds a new Attestation to the SubnetInfo if the attestation's data matches the base one.
-  Assumes that the SubnetInfo already exists.
   """
   @spec add_attestation!(non_neg_integer(), Types.Attestation.t()) :: :ok
-  def add_attestation!(subnet_id, attestation) do
-    subnet_info = fetch_subnet_info!(subnet_id)
-
-    if subnet_info.data == attestation.data do
+  def add_attestation!(subnet_id, %{data: att_data} = attestation) do
+    # TODO: (#1302) On delayed scenarios (past second third of the slot) we could discard useful
+    # messages and end up with empty aggregations due to the subnet not being created yet.
+    with {:ok, subnet_info} <- fetch_subnet_info(subnet_id),
+         ^att_data <- subnet_info.data do
       new_subnet_info = %__MODULE__{
         subnet_info
         | attestations: [attestation | subnet_info.attestations]
@@ -91,12 +91,6 @@ defmodule Types.AttSubnetInfo do
     end
   end
 
-  @spec fetch_subnet_info!(non_neg_integer()) :: t()
-  defp fetch_subnet_info!(subnet_id) do
-    {:ok, subnet_info} = fetch_subnet_info(subnet_id)
-    subnet_info
-  end
-
   @spec delete_subnet(non_neg_integer()) :: :ok
   defp delete_subnet(subnet_id), do: Db.delete(@subnet_prefix <> Integer.to_string(subnet_id))
 
diff --git a/lib/types/sync_subnet_info.ex b/lib/types/sync_subnet_info.ex
index 7bf3c9102..43476d580 100644
--- a/lib/types/sync_subnet_info.ex
+++ b/lib/types/sync_subnet_info.ex
@@ -50,16 +50,15 @@ defmodule Types.SyncSubnetInfo do
 
   @doc """
   Adds a new SyncCommitteeMessage to the SubnetInfo if the message's data matches the base one.
-  Assumes that the SubnetInfo already exists.
   """
   @spec add_message!(non_neg_integer(), Types.SyncCommitteeMessage.t()) :: :ok
-  def add_message!(
-        subnet_id,
-        %Types.SyncCommitteeMessage{slot: slot, beacon_block_root: root} = message
-      ) do
-    subnet_info = fetch_subnet_info!(subnet_id)
+  def add_message!(subnet_id, %Types.SyncCommitteeMessage{} = message) do
+    %{slot: slot, beacon_block_root: root} = message
 
-    if subnet_info.data == {slot, root} do
+    # TODO: (#1302) On delayed scenarios (past second third of the slot) we could discard useful
+    # messages and end up with empty aggregations due to the subnet not being created yet.
+    with {:ok, subnet_info} <- fetch_subnet_info(subnet_id),
+         {^slot, ^root} <- subnet_info.data do
       new_subnet_info = %__MODULE__{
         subnet_info
         | messages: [message | subnet_info.messages]
@@ -100,12 +99,6 @@ defmodule Types.SyncSubnetInfo do
     end
   end
 
-  @spec fetch_subnet_info!(non_neg_integer()) :: t()
-  defp fetch_subnet_info!(subnet_id) do
-    {:ok, subnet_info} = fetch_subnet_info(subnet_id)
-    subnet_info
-  end
-
   @spec delete_subnet(non_neg_integer()) :: :ok
   defp delete_subnet(subnet_id), do: Db.delete(@subnet_prefix <> Integer.to_string(subnet_id))