diff --git a/tests/coordinator/src/tests/mod.rs b/tests/coordinator/src/tests/mod.rs
index 5ee2ce3c..0e07d835 100644
--- a/tests/coordinator/src/tests/mod.rs
+++ b/tests/coordinator/src/tests/mod.rs
@@ -10,6 +10,9 @@ pub use key_gen::key_gen;
 mod batch;
 pub use batch::batch;
 
+mod sign;
+pub use sign::sign;
+
 pub(crate) const COORDINATORS: usize = 4;
 pub(crate) const THRESHOLD: usize = ((COORDINATORS * 2) / 3) + 1;
 
diff --git a/tests/coordinator/src/tests/sign.rs b/tests/coordinator/src/tests/sign.rs
new file mode 100644
index 00000000..00439029
--- /dev/null
+++ b/tests/coordinator/src/tests/sign.rs
@@ -0,0 +1,349 @@
+use std::{
+  time::Duration,
+  collections::{HashSet, HashMap},
+};
+
+use zeroize::Zeroizing;
+use rand_core::{RngCore, OsRng};
+
+use ciphersuite::{group::GroupEncoding, Ciphersuite, Secp256k1};
+
+use dkg::Participant;
+
+use serai_client::{
+  PairTrait, PairSigner,
+  primitives::{
+    NetworkId, Coin, Amount, Balance, BlockHash, SeraiAddress, ExternalAddress,
+    insecure_pair_from_name,
+  },
+  tokens::{
+    primitives::{OutInstruction, OutInstructionWithBalance},
+    TokensEvent,
+  },
+  in_instructions::primitives::{InInstruction, InInstructionWithBalance, Batch},
+};
+use messages::{sign::SignId, SubstrateContext, CoordinatorMessage};
+
+use crate::{*, tests::*};
+
+pub async fn sign<C: Ciphersuite>(
+  processors: &mut [Processor],
+  network_key: &Zeroizing<C::F>,
+  plan_id: [u8; 32],
+) {
+  let id = SignId {
+    key: (C::generator() * **network_key).to_bytes().as_ref().to_vec(),
+    id: plan_id,
+    attempt: 0,
+  };
+
+  // Select a random participant to exclude, so we know for sure who *is* participating
+  assert_eq!(COORDINATORS - THRESHOLD, 1);
+  let excluded_signer =
+    usize::try_from(OsRng.next_u64() % u64::try_from(processors.len()).unwrap()).unwrap();
+  for (i, processor) in processors.iter_mut().enumerate() {
+    if i == excluded_signer {
+      continue;
+    }
+
+    processor
+      .send_message(messages::sign::ProcessorMessage::Preprocess {
+        id: id.clone(),
+        preprocess: [u8::try_from(i).unwrap(); 64].to_vec(),
+      })
+      .await;
+  }
+  // Before this plan is signed, the Tributary will agree the triggering Substrate block occurred,
+  // adding an extra step of latency
+  wait_for_tributary().await;
+  wait_for_tributary().await;
+
+  // Send from the excluded signer so they don't stay stuck
+  processors[excluded_signer]
+    .send_message(messages::sign::ProcessorMessage::Preprocess {
+      id: id.clone(),
+      preprocess: [u8::try_from(excluded_signer).unwrap(); 64].to_vec(),
+    })
+    .await;
+
+  // Read from a known signer to find out who was selected to sign
+  let known_signer = (excluded_signer + 1) % COORDINATORS;
+  let participants = match processors[known_signer].recv_message().await {
+    CoordinatorMessage::Sign(messages::sign::CoordinatorMessage::Preprocesses {
+      id: this_id,
+      preprocesses,
+    }) => {
+      assert_eq!(&id, &this_id);
+      assert_eq!(preprocesses.len(), THRESHOLD - 1);
+      assert!(!preprocesses
+        .contains_key(&Participant::new(u16::try_from(known_signer).unwrap() + 1).unwrap()));
+
+      let mut participants =
+        preprocesses.keys().map(|p| usize::from(u16::from(*p)) - 1).collect::<HashSet<_>>();
+      for (p, preprocess) in preprocesses {
+        assert_eq!(preprocess, vec![u8::try_from(u16::from(p)).unwrap() - 1; 64]);
+      }
+      participants.insert(known_signer);
+      participants
+    }
+    _ => panic!("coordinator didn't send back Preprocesses"),
+  };
+
+  for i in participants.clone() {
+    if i == known_signer {
+      continue;
+    }
+
+    let processor = &mut processors[i];
+    let mut preprocesses = participants
+      .clone()
+      .into_iter()
+      .map(|i| {
+        (
+          Participant::new(u16::try_from(i + 1).unwrap()).unwrap(),
+          [u8::try_from(i).unwrap(); 64].to_vec(),
+        )
+      })
+      .collect::<HashMap<_, _>>();
+    preprocesses.remove(&Participant::new(u16::try_from(i + 1).unwrap()).unwrap());
+
+    assert_eq!(
+      processor.recv_message().await,
+      CoordinatorMessage::Sign(messages::sign::CoordinatorMessage::Preprocesses {
+        id: id.clone(),
+        preprocesses
+      })
+    );
+  }
+
+  for i in participants.clone() {
+    let processor = &mut processors[i];
+    processor
+      .send_message(messages::sign::ProcessorMessage::Share {
+        id: id.clone(),
+        share: vec![u8::try_from(i).unwrap(); 32],
+      })
+      .await;
+  }
+  wait_for_tributary().await;
+  for i in participants.clone() {
+    let processor = &mut processors[i];
+    let mut shares = participants
+      .clone()
+      .into_iter()
+      .map(|i| {
+        (
+          Participant::new(u16::try_from(i + 1).unwrap()).unwrap(),
+          vec![u8::try_from(i).unwrap(); 32],
+        )
+      })
+      .collect::<HashMap<_, _>>();
+    shares.remove(&Participant::new(u16::try_from(i + 1).unwrap()).unwrap());
+
+    assert_eq!(
+      processor.recv_message().await,
+      CoordinatorMessage::Sign(messages::sign::CoordinatorMessage::Shares {
+        id: id.clone(),
+        shares,
+      })
+    );
+  }
+
+  // TODO: Completed flow
+}
+
+#[tokio::test]
+async fn sign_test() {
+  let (processors, test) = new_test();
+
+  test
+    .run_async(|ops| async move {
+      // Wait for the Serai node to boot, and for the Tendermint chain to get past the first block
+      // TODO: Replace this with a Coordinator RPC
+      tokio::time::sleep(Duration::from_secs(150)).await;
+
+      // Sleep even longer if in the CI due to it being slower than commodity hardware
+      if std::env::var("GITHUB_CI") == Ok("true".to_string()) {
+        tokio::time::sleep(Duration::from_secs(120)).await;
+      }
+
+      // Connect to the Message Queues as the processor
+      let mut new_processors: Vec<Processor> = vec![];
+      for (handles, key) in processors {
+        new_processors.push(Processor::new(NetworkId::Bitcoin, &ops, handles, key).await);
+      }
+      let mut processors = new_processors;
+
+      let (substrate_key, network_key) = key_gen::<Secp256k1>(&mut processors).await;
+
+      // 'Send' external coins into Serai
+      let serai = processors[0].serai().await;
+      let (serai_pair, serai_addr) = {
+        let mut name = [0; 4];
+        OsRng.fill_bytes(&mut name);
+        let pair = insecure_pair_from_name(&hex::encode(name));
+        let address = SeraiAddress::from(pair.public());
+
+        // Fund the new account to pay for fees
+        serai
+          .publish(
+            &serai
+              .sign(
+                &PairSigner::new(insecure_pair_from_name("Ferdie")),
+                &Serai::transfer_sri(address, Amount(1_000_000_000)),
+                0,
+                Default::default(),
+              )
+              .unwrap(),
+          )
+          .await
+          .unwrap();
+
+        (PairSigner::new(pair), address)
+      };
+
+      #[allow(clippy::inconsistent_digit_grouping)]
+      let amount = Amount(1_000_000_00);
+      let balance = Balance { coin: Coin::Bitcoin, amount };
+
+      let coin_block = BlockHash([0x33; 32]);
+      let block_included_in = batch::<Secp256k1>(
+        &mut processors,
+        &substrate_key,
+        &network_key,
+        Batch {
+          network: NetworkId::Bitcoin,
+          id: 0,
+          block: coin_block,
+          instructions: vec![InInstructionWithBalance {
+            instruction: InInstruction::Transfer(serai_addr),
+            balance,
+          }],
+        },
+      )
+      .await;
+
+      let block_included_in_hash =
+        serai.get_block_by_number(block_included_in).await.unwrap().unwrap().hash();
+
+      assert_eq!(
+        serai.get_sri_balance(block_included_in_hash, serai_addr).await.unwrap(),
+        1_000_000_000
+      );
+
+      // Verify the mint occurred as expected
+      assert_eq!(
+        serai.get_mint_events(block_included_in_hash).await.unwrap(),
+        vec![TokensEvent::Mint { address: serai_addr, balance }]
+      );
+      assert_eq!(
+        serai.get_token_supply(block_included_in_hash, Coin::Bitcoin).await.unwrap(),
+        amount
+      );
+      assert_eq!(
+        serai.get_token_balance(block_included_in_hash, Coin::Bitcoin, serai_addr).await.unwrap(),
+        amount
+      );
+
+      // Trigger a burn
+      let out_instruction =
+        OutInstruction { address: ExternalAddress::new(b"external".to_vec()).unwrap(), data: None };
+      serai
+        .publish(
+          &serai
+            .sign(
+              &serai_pair,
+              &Serai::burn(balance, out_instruction.clone()),
+              0,
+              Default::default(),
+            )
+            .unwrap(),
+        )
+        .await
+        .unwrap();
+
+      // TODO: We *really* need a helper for this pattern
+      let mut last_serai_block = block_included_in;
+      'outer: for _ in 0 .. 20 {
+        tokio::time::sleep(Duration::from_secs(6)).await;
+        if std::env::var("GITHUB_CI") == Ok("true".to_string()) {
+          tokio::time::sleep(Duration::from_secs(6)).await;
+        }
+
+        while last_serai_block <= serai.get_latest_block().await.unwrap().number() {
+          let burn_events = serai
+            .get_burn_events(
+              serai.get_block_by_number(last_serai_block).await.unwrap().unwrap().hash(),
+            )
+            .await
+            .unwrap();
+
+          if !burn_events.is_empty() {
+            assert_eq!(burn_events.len(), 1);
+            assert_eq!(
+              burn_events[0],
+              TokensEvent::Burn {
+                address: serai_addr,
+                balance,
+                instruction: out_instruction.clone()
+              }
+            );
+            break 'outer;
+          }
+          last_serai_block += 1;
+        }
+      }
+
+      let last_serai_block = serai.get_block_by_number(last_serai_block).await.unwrap().unwrap();
+      let last_serai_block_hash = last_serai_block.hash();
+      assert_eq!(
+        serai.get_token_supply(last_serai_block_hash, Coin::Bitcoin).await.unwrap(),
+        Amount(0)
+      );
+      assert_eq!(
+        serai.get_token_balance(last_serai_block_hash, Coin::Bitcoin, serai_addr).await.unwrap(),
+        Amount(0)
+      );
+
+      let mut plan_id = [0; 32];
+      OsRng.fill_bytes(&mut plan_id);
+      let plan_id = plan_id;
+
+      // We should now get a SubstrateBlock
+      for processor in processors.iter_mut() {
+        assert_eq!(
+          processor.recv_message().await,
+          messages::CoordinatorMessage::Substrate(
+            messages::substrate::CoordinatorMessage::SubstrateBlock {
+              context: SubstrateContext {
+                serai_time: last_serai_block.time().unwrap() / 1000,
+                network_latest_finalized_block: coin_block,
+              },
+              network: NetworkId::Bitcoin,
+              block: last_serai_block.number(),
+              key: (Secp256k1::generator() * *network_key).to_bytes().to_vec(),
+              burns: vec![OutInstructionWithBalance {
+                instruction: out_instruction.clone(),
+                balance: Balance { coin: Coin::Bitcoin, amount }
+              }],
+              batches: vec![],
+            }
+          )
+        );
+
+        // Send the ACK, claiming there's a plan to sign
+        processor
+          .send_message(messages::ProcessorMessage::Coordinator(
+            messages::coordinator::ProcessorMessage::SubstrateBlockAck {
+              network: NetworkId::Bitcoin,
+              block: last_serai_block.number(),
+              plans: vec![plan_id],
+            },
+          ))
+          .await;
+      }
+
+      sign::<Secp256k1>(&mut processors, &network_key, plan_id).await;
+    })
+    .await;
+}