In our interconnected digital world, the need for seamless and reliable data exchange is paramount, and the transport layer is where this crucial work is done, acting as the logical communication bridge between application processes. This chapter provides a fundamental overview of the transport layer. It begins by introducing computer networks, their history, and layered models (e.g., OSI). The focus is on defining the transport layer, its core protocols (TCP, UDP, and QUIC), key technologies (connection management, reliable transmission, flow and congestion control), and the protocol evolution path, including the paradigm shift toward future network architectures. Through packet capture experiments and exercises, students will deepen their understanding of these protocols.