Duplex scanning is a feature of some computer scanners and multifunction printers that support duplex printing. It refers to the scanners ability to scan both sides of a sheet of paper simultaneously. Scanners without this capability can only scan both sides of a sheet of paper by reinserting it manually the other way up. Duplex scanning is usually implemented on multifunction printers using a Reversing Automatic Document Feeder (RADF), which removes, reverses, and re-feeds the document after scanning one side. Duplex scanning is achieved on scanners by either RADF or by single pass duplex scanning using two cameras, one for each side of the document; two-camera scanners scan twice as fast as a similar two-pass scanner.

There are two ways for duplex scanning to occur, including a scanners use of two cameras or its ability to flip the paper. If two cameras are in the duplex scanner, one on the top and one on the bottom, then each can individually scan a side of the paper. The other way is to scan the first side, use the document handler to flip the paper over, and then scan the second side. Both are effective, but the latter tends to be a bit cheaper because less hardware is needed.

Duplex scanning is not as common as simplex scanning, which just scans one side of a sheet. Duplex scanning is most often found on duplex multifunction printers (MFPs), though there are some stand-alone scanners that also have this feature. The user usually can switch between duplex and simplex scanning, and the only real advantage is seen in time savings, because this type of scan often takes less time and effort.

Duplex scanning is not only used for scanning documents, but it is also used in medical procedures such as duplex ultrasound. Duplex ultrasound involves using high-frequency sound waves to look at the speed of blood flow and structure of the leg veins. The term "duplex" refers to the fact that two modes of imaging are used: B-mode and Doppler.