This document provides an introduction to data communications and networks. It discusses the key topics of components of data communication, data representation, data flow, network criteria including performance, reliability and security, physical network structures including topologies, categories of networks such as LAN, WAN, MAN, the history and structure of the Internet, and protocols and standards for communication. Figures and diagrams are included to illustrate network topologies, categories of networks, examples of WAN structures, and the hierarchical organization of the Internet.