Check 21 is the common name for the Check Clearing for the 21st Century Act. It's new legislation that was recently passed by congress and made a law when signed by the President of the United States (remember "I'm just a bill" from Saturday morning cartoons). Check 21 basically streamlines the traditional check processing system by incorporating new electronic technology. This new system replaces an outdated check clearing system that banks and other financial institutions have used for many years. The advantage is the ability to cut the time it takes for a check to clear from days to hours.

The process to do this involves a pseudo or substitute check. Check 21 now allows banks to use this in place of original checks. The technique to make this a reality involves converting the information on the check into an electronic file, which is then sent to the maker's financial institution for payment. This significantly speeds up the check clearing process from days to hours. The original check can even be destroyed because a substitute check can be made at any time during the process. This image can be used as a proof of payment just like an original check. In fact the checks look almost exactly like original checks except for a slightly reduced image of both the front and back of the original check.

You can expect to see a substitute check if the original check was converted to an electronic file during the payment process and the check turns out to be a bad check due to non-sufficient funds in the payee