A routing number, also known as an ABA number or RTN, is a nine-digit code assigned to each financial institution in the United States. It is used to identify the institution and facilitate the electronic transfer of funds between banks. For instance, the routing number for Wells Fargo in California is 121000248.
Routing numbers play a crucial role in the banking system, enabling seamless and secure transactions between accounts and institutions. Historically, the adoption of automated clearing houses (ACHs) in the 1970s led to the widespread use of routing numbers, streamlining the process of electronic fund transfers.