This document provides an overview of Web OPAC (Online Public Access Catalog). It begins by explaining how OPAC systems improved upon traditional card catalogs by allowing users to search library collections via computer. It then defines key terms like catalog, OPAC, and Web OPAC. The document discusses the history of OPAC systems from 1st to 3rd generation and compares features of OPAC and Web OPAC. It also outlines searching capabilities, access points, advantages, and limitations of Web OPAC before concluding with examples of Web OPAC implementations in India.