The Physical Layer is the first layer of the OSI model, responsible for transmitting raw data bits over a physical medium. It defines the electrical, mechanical, and procedural aspects of communication, including the types of cables, connectors, and signaling methods used. This layer ensures that data is sent and received accurately between devices. In addition to cables, the Physical Layer also encompasses wireless transmission methods, such as radio waves and infrared signals. It plays a crucial role in determining the speed and distance of data transmission, impacting overall network performance and reliability.