diff --git a/SwiftChain/Models/Block.swift b/SwiftChain/Models/Block.swift
index fd4c083..53abb02 100644
--- a/SwiftChain/Models/Block.swift
+++ b/SwiftChain/Models/Block.swift
@@ -9,7 +9,7 @@
 import Foundation
 import CryptoSwift
 
-class Block {
+class Block: Codable {
     var hash: String
     var transactions: [Transaction]
     var previousHash: String
@@ -19,6 +19,10 @@ class Block {
     var difficulty: Int
     var miner: String? // Adresse qui recevra la récompense
 
+    enum CodingKeys: String, CodingKey {
+        case hash, transactions, previousHash, index, nonce, timestamp, difficulty, miner
+    }
+
     init(hash: String = "", transactions: [Transaction] = [], previousHash: String = "",
          index: Int = 0, nonce: Int = 0, timestamp: Int = 0, difficulty: Int = 4) {
         self.hash = hash
@@ -30,6 +34,30 @@ class Block {
         self.difficulty = difficulty
     }
 
+    required init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+        hash = try container.decode(String.self, forKey: .hash)
+        transactions = try container.decode([Transaction].self, forKey: .transactions)
+        previousHash = try container.decode(String.self, forKey: .previousHash)
+        index = try container.decode(Int.self, forKey: .index)
+        nonce = try container.decode(Int.self, forKey: .nonce)
+        timestamp = try container.decode(Int.self, forKey: .timestamp)
+        difficulty = try container.decode(Int.self, forKey: .difficulty)
+        miner = try container.decodeIfPresent(String.self, forKey: .miner)
+    }
+
+    func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+        try container.encode(hash, forKey: .hash)
+        try container.encode(transactions, forKey: .transactions)
+        try container.encode(previousHash, forKey: .previousHash)
+        try container.encode(index, forKey: .index)
+        try container.encode(nonce, forKey: .nonce)
+        try container.encode(timestamp, forKey: .timestamp)
+        try container.encode(difficulty, forKey: .difficulty)
+        try container.encodeIfPresent(miner, forKey: .miner)
+    }
+
     func mineBlock() -> Double {
         let startTime = Date()
         let target = String(repeating: "0", count: difficulty)
diff --git a/SwiftChain/Models/Blockchain.swift b/SwiftChain/Models/Blockchain.swift
index 0df73f0..a48f6a3 100644
--- a/SwiftChain/Models/Blockchain.swift
+++ b/SwiftChain/Models/Blockchain.swift
@@ -116,4 +116,62 @@ class Blockchain {
         }
         return true
     }
+
+    func validateChain(_ newChain: [Block]) -> Bool {
+        // Vérifier que la chaîne commence par notre genesis block
+        guard newChain.first?.hash == chain.first?.hash else {
+            print("Genesis block mismatch")
+            return false
+        }
+
+        // Vérifier chaque bloc
+        for i in 1..<newChain.count {
+            let block = newChain[i]
+            let previousBlock = newChain[i-1]
+
+            // Vérifier le chaînage
+            if block.previousHash != previousBlock.hash {
+                print("Invalid chain at block \(i): incorrect previous hash")
+                return false
+            }
+
+            // Vérifier la validité du bloc
+            if !block.isValid() {
+                print("Invalid chain at block \(i): invalid block hash")
+                return false
+            }
+        }
+
+        return true
+    }
+
+    func replaceChain(_ newChain: [Block]) -> Bool {
+        // Vérifier que la nouvelle chaîne est plus longue
+        guard newChain.count > chain.count else {
+            print("Received chain is not longer than current chain")
+            return false
+        }
+
+        // Vérifier la validité de la nouvelle chaîne
+        guard validateChain(newChain) else {
+            print("Received chain is invalid")
+            return false
+        }
+
+        // Sauvegarder l'ancienne chaîne au cas où
+        let oldChain = chain
+
+        // Essayer de traiter tous les blocs
+        for block in newChain {
+            if !accountManager.processBlock(block) {
+                print("Failed to process transactions in block \(block.index)")
+                chain = oldChain
+                return false
+            }
+        }
+
+        chain = newChain
+        print("Chain replaced successfully")
+        return true
+    }
 }
diff --git a/SwiftChain/Models/MemPool.swift b/SwiftChain/Models/MemPool.swift
index 1e4edee..ea92ccc 100644
--- a/SwiftChain/Models/MemPool.swift
+++ b/SwiftChain/Models/MemPool.swift
@@ -94,4 +94,37 @@ class MemPool {
     func getAllPendingTransactions() -> [Transaction] {
         return pendingTransactions
     }
+
+    /**
+     * Nettoie le mempool en retirant les transactions qui sont dans la chaîne
+     */
+    func cleanupMempool(chain: [Block]) {
+        var remainingTransactions: [Transaction] = []
+
+        for pendingTx in pendingTransactions {
+            // On vérifie si la transaction est dans un des blocs
+            var isInChain = false
+
+            for block in chain {
+                if block.transactions.contains(where: { chainTx in
+                    chainTx.sender == pendingTx.sender &&
+                    chainTx.receiver == pendingTx.receiver &&
+                    chainTx.amount == pendingTx.amount &&
+                    chainTx.type == pendingTx.type
+                }) {
+                    isInChain = true
+                    break
+                }
+            }
+
+            // Si la transaction n'est pas dans la chaîne, on la garde
+            if !isInChain {
+                remainingTransactions.append(pendingTx)
+            }
+        }
+
+        // Mettre à jour les transactions en attente
+        print("Mempool cleanup: removed \(pendingTransactions.count - remainingTransactions.count) transactions")
+        pendingTransactions = remainingTransactions
+    }
 }
diff --git a/SwiftChain/Models/Node.swift b/SwiftChain/Models/Node.swift
index ac4ce1d..a8759ca 100644
--- a/SwiftChain/Models/Node.swift
+++ b/SwiftChain/Models/Node.swift
@@ -24,6 +24,9 @@ class Node {
 
     enum MessageType: String, Codable {
         case transaction = "TX"
+        case blockchainRequest = "BC_REQ"
+        case blockchainResponse = "BC_RES"
+        case newBlock = "NEW_BLOCK"
     }
 
     struct NetworkMessage: Codable {
@@ -152,21 +155,146 @@ class Node {
             case .transaction:
                 let transaction = try JSONDecoder().decode(Transaction.self, from: message.data)
                 print("Transaction decoded: \(transaction.sender) -> \(transaction.receiver): \(transaction.amount)")
-
                 if blockchain.submitTransaction(transaction) {
                     print("Transaction added to mempool successfully")
                 } else {
                     print("Failed to add transaction to mempool")
                 }
+
+            case .blockchainRequest:
+                // Envoyer notre blockchain au pair
+                sendBlockchain(to: connection)
+
+            case .blockchainResponse:
+                // Recevoir et traiter la blockchain
+                let receivedChain = try JSONDecoder().decode([Block].self, from: message.data)
+                handleReceivedBlockchain(receivedChain)
+
+            case .newBlock:
+                // Recevoir et traiter un nouveau bloc
+                let block = try JSONDecoder().decode(Block.self, from: message.data)
+                handleReceivedBlock(block)
             }
         } catch {
             print("Failed to decode received data: \(error)")
         }
     }
 
+    // Quand un pair se connecte, demander sa blockchain
     private func handleNewConnection(_ connection: NWConnection) {
         connection.start(queue: queue)
         peers.append(connection)
         startReceiving(connection)
+
+        // Demander la blockchain
+        requestBlockchain(from: connection)
+    }
+
+    private func requestBlockchain(from peer: NWConnection) {
+        do {
+            let message = NetworkMessage(type: .blockchainRequest, data: Data())
+            let messageData = try JSONEncoder().encode(message)
+
+            peer.send(content: messageData, completion: .contentProcessed { error in
+                if let error = error {
+                    print("Failed to request blockchain: \(error)")
+                } else {
+                    print("Blockchain request sent to: \(peer.endpoint)")
+                }
+            })
+        } catch {
+            print("Failed to encode blockchain request: \(error)")
+        }
+    }
+
+    private func sendBlockchain(to peer: NWConnection) {
+        do {
+            let chainData = try JSONEncoder().encode(blockchain.chain)
+            let message = NetworkMessage(type: .blockchainResponse, data: chainData)
+            let messageData = try JSONEncoder().encode(message)
+
+            peer.send(content: messageData, completion: .contentProcessed { error in
+                if let error = error {
+                    print("Failed to send blockchain: \(error)")
+                } else {
+                    print("Blockchain sent to: \(peer.endpoint)")
+                }
+            })
+        } catch {
+            print("Failed to encode blockchain: \(error)")
+        }
+    }
+
+    private func handleReceivedBlockchain(_ receivedChain: [Block]) {
+        print("Received blockchain with \(receivedChain.count) blocks")
+
+        // Vérifier si la chaîne reçue est plus longue et valide
+        if receivedChain.count > blockchain.chain.count {
+            print("Received chain is longer, validating...")
+            if blockchain.replaceChain(receivedChain) {
+                print("Blockchain updated successfully")
+                // Nettoyer le mempool des transactions qui sont maintenant dans la chaîne
+                blockchain.memPool.cleanupMempool(chain: receivedChain)
+            } else {
+                print("Failed to update blockchain")
+            }
+        } else {
+            print("Current chain is longer or equal, keeping it")
+        }
+    }
+
+    private func handleReceivedBlock(_ block: Block) {
+        print("Received new block: \(block.hash)")
+
+        // Vérifier que le bloc suit bien notre dernier bloc
+        guard let lastBlock = blockchain.chain.last else {
+            print("No existing chain")
+            return
+        }
+
+        if block.previousHash != lastBlock.hash {
+            print("Block does not connect to our chain")
+            return
+        }
+
+        if !block.isValid() {
+            print("Block is not valid")
+            return
+        }
+
+        // Traiter les transactions du bloc
+        if !blockchain.accountManager.processBlock(block) {
+            print("Failed to process block transactions")
+            return
+        }
+
+        // Ajouter le bloc à la chaîne
+        blockchain.chain.append(block)
+        print("New block added to chain")
+
+        // Propager le bloc aux autres pairs (sauf celui qui nous l'a envoyé)
+        broadcastBlock(block)
+    }
+
+    private func broadcastBlock(_ block: Block) {
+        do {
+            let blockData = try JSONEncoder().encode(block)
+            let message = NetworkMessage(type: .newBlock, data: blockData)
+            let messageData = try JSONEncoder().encode(message)
+
+            print("Broadcasting block to peers")
+
+            for peer in peers {
+                peer.send(content: messageData, completion: .contentProcessed { error in
+                    if let error = error {
+                        print("Failed to send block: \(error)")
+                    } else {
+                        print("Block sent successfully to: \(peer.endpoint)")
+                    }
+                })
+            }
+        } catch {
+            print("Failed to encode block: \(error)")
+        }
     }
 }