1. Introduction

Cloud computing has evolved through various phases from distributed computing, mobile computing, grid computing and currently is in most evolved form of the computing. Cloud computing is basically a business model where various hardware resources such as CPU, network, storage and software resources such as platform, applications are available on demand and are offered as utility; i.e., a Cloud user has to pay for the usage of the Cloud resources. The proliferation of the Internet has made possible the availability of the Cloud services across the globe, though private Cloud exists on intranet. As Cloud is a business model, a large number of players have joined the Cloud platform with their services. Recently, a tough competition has been noticed in the Cloud market for the offered services as both the number of providers and customers have increased to a large extent. Though it creates a good opportunity for both provider and customer, it also results in a number of issues to be addressed properly to make the Cloud market more beneficial for the customer and the provider. This chapter takes a look at widely accepted Cloud computing definitions, explains its concepts and summarizes various services and deployment models of Cloud computing. This chapter also gives an overview of benefits and challenges of the Cloud computing. Further, it describes pricing in detail to understand the need for auction of the Cloud resources followed by a mention on the organization of the book. The aim of this chapter is to offer a prerequisite to understand the concepts discussed further in the book and its role in research.