Cloud computing is a double-edged sword from the privacy and security standpoints. Despite its potential to provide a low cost security, organizations may increase risks by storing sensitive data in the cloud. In this thesis, is analyzed how the cloud’s characteristics such as newness, nature of the architecture, and attractiveness and vulnerability as a cybercrime target are tightly linked to privacy and security. It is tried to approach the issue from both sides, and the one of the user and the one of Cloud Service Provider. Also the XACML language and a policy sample are presented providing that way that XACML policies may help to secure a heterogeneous environment as the one of Cloud computing.