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RS-422 is the electrical specification of a 4-wire full-duplex serial data connection. Full-duplex means that data can flow both ways at the same time. Data is conveyed by the difference in voltage level between the each pair of wires, and is therefore resilient against noise and other interference.

RS-422 allows several receivers to be active at one time but only one driver. It is therefore a multi-drop system and not a true multi-point system.

RS is an abbreviation for "Recommended Standard" as was defined by the Electronics Industries Association (EIA) of the USA, although today the standard is formally known as EIA-422.

The RS-422 communications standard provides certain important benefits in relation to the earlier RS-232 standard. The most significant improvement is the use of differential signalling, where the data is conveyed as a difference in voltage level between two wires, and not just as a voltage with reference to ground, as was the case with RS-232.

This improvement allows the transmission of data over simple twisted pair cable at data rates of up to 10 Mbit/s over short distances (1m), or up to 100 kbit/s over longer distances (1000m).

Another advantage offered by RS-422 over RS-232 is the fact that one driver can communicate over a common connection with up to 10 receivers, thus defining RS-422 a multi-drop standard.

RS-422 has not been widely adopted because it has been superceeded by the true multi-point standard RS-485, which shares the same differential signalling system but uses only two wires (half-duplex).

RS-422 can interoperate with RS-485 subject to certain restrictions.