An ABA number, also known as a routing number or routing transfer number, is a sequence of nine numeric characters used by banks to identify specific financial institutions responsible for the payment of a negotiable instrument. It was developed by the American Bankers Association in 1910 to identify check processing endpoints, but it has evolved to designate participants in automated clearinghouses, electronic funds transfer, and online banking. An ABA routing number can be issued only to a federal or state-chartered financial institution that has been determined to be eligible for a master account by a Federal Reserve Bank.

The ABA routing number is the left-most number at the bottom of a check, followed by the account number, and then by the number of the check. It is used to identify banks in the United States and helps banks in the process of transferring money domestically between accounts for different kinds of transactions, such as direct deposit or bank transfers. ABA numbers are important because they identify financial institutions for processing payments and making direct deposits.

To find your ABA routing number, you can check the bottom of your checks, log into your online banking account, or use your banks mobile app. The ABA number is made up of five parts, each with its own purpose: the first four digits represent the banks physical location, and the fifth and sixth digits represent the Federal Reserve Bank district where the bank is located.