This document provides an overview of computer networks and the Internet. It describes the nuts and bolts view of the basic components including end systems, communication links, routers, packets, and protocols. It also describes the service oriented view in which the Internet provides distributed applications with either a connection oriented reliable service or a connectionless unreliable service. Finally, it discusses network cores including circuit switching which reserves bandwidth for a call, and packet switching which transmits data in packets and allows statistical multiplexing and sharing of bandwidth.