Cross-Chain Message Passing (XCMP) is Polkadot’s secure and efficient protocol for enabling parachains to exchange data and tokens without relying on centralised intermediaries. Unlike traditional bridges, which require trusted validators, XCMP leverages Polkadot’s shared security model and relay chain to facilitate trustless communication. Here’s how it works:

Message Queues & Relay Chain Coordination – Parachains submit messages (e.g., token transfers or smart contract calls) to a Merkle tree-based queue. The relay chain validates and routes these messages but does not store their content, ensuring scalability.

Collator Node Role – Collators (parachain-specific nodes) gather and forward messages between chains, ensuring delivery while validators on the relay chain verify correctness.

HRMP (Horizontal Relay-routed Message Passing) – A temporary, more resource-intensive version of XCMP, HRMP allows parachains to communicate via the relay chain until XCMP is fully optimised for lower latency and higher throughput.

XCMP’s design eliminates the need for wrapped assets or third-party bridges, reducing security risks. It enables seamless interoperability, letting decentralised applications (dApps) on one parachain trigger actions on another—for example, a DeFi protocol on Acala could interact with a gaming NFT on Moonbeam. By enabling scalable, trustless cross-chain communication, XCMP is central to Polkadot’s vision of a unified multi-chain ecosystem.