Collators are full nodes that exist on both the parachains and the main relay chain of the Polkadot Network. Their primary goal is to keep parachains (sovereign blockchains or specialized shards) running by collecting parachain transactions and producing state transition proofs (basically machine-driven progress reports) for validators on the Relay Chain. Collators, like miners in a proof-of-work system, have access to all state transition information required for authoring new blocks and executing transactions. Collators are also used to send and receive messages from other parachains, facilitating communication through Cross-Chain Message Passing (XCMP).