TWAIN is a standard software protocol and applications programming interface (API) designed to facilitate and regulate communication between software applications and imaging devices such as scanners.

Even though it is widely known as "Technology Without An Interesting Name", TWAIN is not an official acronym. BoardBoss has this on good authority as he knows a founding member of the TWAIN Working Group.

The word TWAIN is from Rudyard Kipling's "The Ballad of East and West"—"...and never the twain shall meet..."—reflecting the difficulties encountered when first attempting to connect scanners and personal computers. It has since been up-cased to TWAIN to make it more distinctive.

The early objectives for TWAIN drivers, which were simply to get hardware and software "talking", were frequently problematic. Therefore, considerations such as improved performance/throughput were not paramount, if they were even considered at all. TWAIN should never be confused with ISIS drivers as the two are vastly different. Please see ISIS Drivers elsewhere in this section.

TWAIN is what enables most entry- and mid-level scanners and computer applications (i.e. Microsoft Word, Adobe Photoshop, etc.) to communicate. The TWAIN driver, also known as a device driver, is virtually always provided by the manufacturer of the hardware (scanner).