Since last decade, Cloud computing has become a formal area of research in Computer Science. It is the next generation architecture for IT Enterprises, and has proliferated itself due to the benefits it gives. Cloud computing offers the solution for carrying out efficient, scalable and low cost computing.It supports access mobility, easier maintenance, scalability and operability in terms of its management and usage. Because of the services and solutions, it provides the industry a next generation computing which is vulnerable to a range of known and unknown attacks from attackers. Securing a trustworthy Cloud environment is a serious problem that needs urgent attention. This book focuses on taxonomy of possible attacks on a Cloud environment and taxonomy of the defense.The attack taxonomy describes existing threats on Cloud security, whereas the defense taxonomy gives a classification of the various counter measures that can be taken to protect the Cloud environment from such attacks. This analysis will provide the researchers, academicians and industry a better understanding of cloud computing fundamentals along with existing attacks and defense mechanisms on Cloud security.