Medium access control (MAC) is the sublayer of the data link layer that coordinates use of a shared medium in wireless networks. It addresses problems like hidden and exposed terminals through techniques like carrier sense multiple access (CSMA) and time division multiple access (TDMA). Early MAC protocols like Aloha and slotted Aloha had low throughput due to collisions from lack of coordination, while later protocols use mechanisms like reservations, polling, and orthogonal codes to coordinate access and avoid collisions.