Carrier-sense multiple access with collision avoidance (CSMA/CA) in computer networking, is a network multiple access method in which carrier sensing is used, but nodes attempt to avoid collisions by beginning transmission only after the channel is sensed to be "idle". When they do transmit, nodes transmit their packet data in its entirety.

It is particularly important for wireless networks, where the alternative with collision detection CSMA/CD, is not possible due to wireless transmitters desensing (turning off) their receivers during packet transmission.

CSMA/CA is unreliable due to the hidden node problem.

CSMA/CA is a protocol that operates in the data link layer (Layer 2) of the OSI model.