What is a bank account routing number?

The bank routing number is a nine-digit number assigned to a particular financial institution by the American Bankers Association, explains About.com. The number, also known as the ABA number or routing transit number, helps direct money to and from a bank account when writing checks or making ACH payments.

Some large financial institutions have multiple routing numbers for different locations or purposes, notes About.com. Banks often publish routing numbers on their websites. The routing number is the first set of numbers at the bottom left of a paper check. When making electronic payments online, users enter the routing number and the bank account number to correctly direct the funds.