A 9-digit code used to identify a financial institution in a transaction. Each individual institution, such as a bank, has its own routing number. This helps to identify where the money has to be sent to.
One can find a bank's routing number on the bottom of checks. This is printed on checks along with the account number.
Routing numbers are typically used in wire transfers or ACH transactions.
At the level of the Federal Reserve Banks, routing numbers are required to process Fedwire funds transfers and the ACH network requires them to process electronic funds transfers (for example direct deposits and bill payments).