XCM

XCM, or Cross-Consensus Messaging, is a protocol used in the Polkadot and Kusama ecosystems to enable cross-chain communication among different consensus systems, including relay chains, parachains, parathreads, and external bridges. It provides a unified language for encoding cross-chain actions and assets, allowing chains with separate consensus mechanisms to interact in a secure and scalable manner.

XCM messages are carried over Cross-Chain Message Passing (XCMP), which provides the transport layer, while XCM itself defines the content and semantics of what is conveyed. A destination chain’s XCM interpreter executes the received instructions subject to its security model and origin rules. Messages can request asset transfers, calls to runtime functions on the destination chain, or changes to execution context, such as paying for execution or depositing assets into an account.

XCM has evolved to support a broader set of instructions and improved security over time. It operates across parachains that share the Polkadot relay chain’s security model and can interact with external bridges through specialized adapters. The design emphasizes a common, interoperable language that reduces the need for bespoke bridge logic between each pair of chains.

Typical use cases include cross-chain token transfers with asset routing, calling functions on a remote parachain, or coordinating governance and identity-related actions across multiple chains. XCM is intended to enable more complex cross-chain workflows while maintaining a clear security boundary via its origin and asset-handling rules.

In the Polkadot ecosystem, XCM complements XCMP as the messaging standard, enabling interoperable communication across multiple chains while leveraging the shared security of the relay chain.