This document provides an overview of cloud computing. It defines cloud computing and discusses its evolution from mainframe computers to today's cloud models. It describes the key advantages of cloud computing like reduced costs, improved scalability and reliability. It also covers various cloud service models like SaaS, PaaS and IaaS and deployment models including public, private and hybrid clouds. The document discusses opportunities and challenges of cloud computing and highlights advantages like lower computer costs, improved performance, reduced software costs and unlimited storage capacity.