Sort codes are the domestic bank codes used to route money transfers between financial institutions in the United Kingdom, and in the Republic of Ireland. They are six-digit hierarchical numerical addresses that specify clearing banks, clearing systems, regions, large financial institutions, groups of financial institutions and ultimately resolve to individual branches. In the UK they continue to be used to route transactions domestically within clearance organisations and to identify accounts, while in the Republic of Ireland (a founder member of the Euro) they have been deprecated and replaced by the SEPA systems and infrastructure.

Sort codes for Northern Ireland branches of banks (codes beginning with a '9') were registered with the Irish Payment Services Organisation (IPSO) for both Northern Ireland and the Republic. These codes are used in the British clearing system and historically in the Irish system.

The sort code is usually formatted as three pairs of numbers, for example 12-34-56. It identifies both the bank (in the first digit or the first two digits) and the branch where the account is held. Sort codes are encoded into IBANs but are not encoded into BICs.