It is a general term for Services, Software, and Applications etc that may involve delivery of hosted services over the Internet or even Intranet.It should be flexible and simple and quickly deployable, and at the same time being highly scalable and cost-effective.It is a new and still evolving concept but it is leading to a general shift towards next generation data centers hosted by large infrastructure companies such as Amazon, Google, etc.The biggest advantage is that users need not have expertise over the technology and may use cloud computing for reducing upfront capital cost and/or for simplifying their job.Cloud Computing is one of the fastest growing segments of software services. The sector has emerged as an important part of software services over the last few years.Cloud Applications generally use large data centers that host Web Applications and Web services. Anyone with a suitable Internet connection and a standard browser can access a cloud application.Cloud computing helps in minimizing the level of detailed interaction with the underlying technology stack i.e. it does all this in a way that minimizes the interaction with the underlying layers of the technology stack.Cloud computing is more of a process than one set technology and accessed over a network.These services are broadly divided into three categories: Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS) and other recent technologies that rely on the Internet to satisfy the computing needs of users.The platform supports a variety of software including the traditional Java and Linux, Apache,MySQL, PHP (LAMP) stack based applications as well as new architectures such as MapReduce.According to Gartner Says Worldwide Cloud Services Revenue will surpass $56.3 billion in 2009, a 21.3 percent increase from 2008 revenue of $46.4 billion.The market is expected to reach $150.1 billion in 2013.According to IDC “Cloud computing is a broad and diverse phenomenon. Much of the growth represents a transfer of traditional IT services to the new cloud model, but there is also scope for creation of substantial new businesses and revenue streams.