“Check 21” is the common name for the United States’ Check Clearing for the 21st Century Act, a federal law enacted in 2003 that enabled banks to phase out paper check handling by allowing electronic check images (especially TIFF-formatted files) to serve all the same legal roles as original paper checks.

Check 21’s effect on the file transfer industry has been to greatly increase the size of files transmitted through banks, as check images are frequently large and non-compressible.