Cloud computing is one of the megatrends in information technology. The chronological emergence of the cloud, as well as the important underlying technologies, terms, and definitions related to it, are presented in detail. Opportunities for service providers and their customers are explored, along with the risks associated with cloud computing. Additionally, the international auditing standard ISAE 3402 is used to illustrate how these risks can be mitigated. This includes fundamental considerations as well as the content and organizational prerequisites for a successful audit of a service provider based on the current auditing standard. The work presents a proven process for auditing, supplemented by practical examples and useful checklists and templates. It is thus essential reading for those in charge.