The Transmission Control Protocol (TCP) has been the backbone of the Internet for decades, ensuring data reliability in complex network environments. A thorough understanding of this foundational protocol is essential for comprehending modern networks. This chapter details TCP’s fundamental characteristics (connection-oriented, reliable transmission) and primary functions (reliable data delivery, flow control, and congestion control). This chapter analyzes TCP header structure, core mechanisms (connection management via three-way handshake/four-way teardown, data segmentation, sliding window, etc.), advantages and disadvantages, and optimization schemes (TCP Fast Open, selective acknowledgment, BBR congestion control). Finally, it introduces advanced TCP optimizations incorporating network coding within the MIN architecture for future networks. The chapter concludes with a TCP connection management experiment to help students grasp the protocol’s practical operation.