This document provides an overview of computer networks, including definitions, history, purposes, types, and how networks have changed the world. It defines a computer network as a collection of interconnected devices that allow sharing of resources and information. Networks originated in the late 1950s and were developed by the military and for airline reservations. There are three main types of networks based on organization (peer-to-peer and server-based), geography (LAN, WAN, MAN), and computing model (centralized and client-server). Networks now connect computers worldwide, allowing fast transmission of documents and information.