An ABA routing number is a nine-digit code used by financial institutions in the United States to identify other financial institutions. It is printed on the bottom of checks and helps to identify the financial institution on which the check was drawn. The ABA routing number was developed by the American Bankers Association in 1910 and has evolved over the years to designate participants in automated clearinghouses, electronic funds transfer, and online banking. The ABA routing number is the left-most number on a check, followed by the account number, and then by the number of the check. ACH routing numbers are used for electronic transactions between financial institutions, while ABA routing numbers apply to paper checks. Routing numbers are used for paying bills, reordering checks, or setting up a direct deposit with your employer or the IRS. To find your ABA routing number, you can check the bottom of your checks, log into your account and select the desired account, or use the U.S. Bank Mobile App.