Media Access Control (MAC) is a sublayer of the data link layer (Layer 2) in the OSI (Open Systems Interconnection) model that is responsible for controlling how devices on a network gain access to the physical transmission medium. It defines rules and protocols for how data is transmitted between networked devices, ensuring that only one device transmits at a time to avoid collisions and maintain orderly communication.

MAC is especially crucial in shared communication mediums like Ethernet or Wi-Fi, where multiple devices compete to send data over the same channel. To handle this, the MAC sublayer implements addressing and channel access mechanisms. Every device on a network interface card (NIC) is assigned a unique MAC address, a hardware-based identifier used to distinguish it from others on the network. This address plays a critical role in directing frames to the correct destination.

The MAC sublayer also manages collision detection and avoidance, particularly in protocols like CSMA/CD (Carrier Sense Multiple Access with Collision Detection) for wired Ethernet and CSMA/CA (Collision Avoidance) for wireless communication. These mechanisms help regulate traffic and reduce interference between devices attempting to send data at the same time.

One of the primary benefits of the MAC sublayer is its ability to enforce fairness and efficiency in medium usage, supporting scalability in both small and large networks. However, depending on network load and technology, MAC mechanisms can become a performance bottleneck or introduce latency, especially in high-density wireless environments.

In modern networking, MAC is fundamental to technologies like Ethernet (IEEE 802.3), Wi-Fi (IEEE 802.11), and Bluetooth. It operates in close coordination with the Logical Link Control (LLC) sublayer to provide error checking, frame synchronization, and flow control.