A keycard lock is a lock operated by a keycard, a flat, rectangular plastic card. The card typically, but not always, has identical dimensions to that of a credit card or American and EU driver's license. The card stores a physical or digital pattern that the door mechanism accepts before disengaging the lock.

There are several common types of keycards in use, including the mechanical holecard, barcode, magnetic stripe, Wiegand wire embedded cards, smart card (embedded with a read/write electronic microchip), RFID, and NFC proximity cards.

Keycards are frequently used in hotels as an alternative to mechanical keys.

The first commercial use of key cards was to raise and lower the gate at automated parking lots where users paid a monthly fee.