Cloud computing is gaining in importance in the industry, and especially within small- and medium-sized companies due to the many benefits that may be generated in terms of cost savings, faster time to market, scalability, cost flexibility, and the optimization of resources. Today, cloud computing is considered as the next IT revolution, and the number of articles, books, papers, and technical reports flood literature. Within the scope of this book, relevant cloud computing applications for small- and medium- sized companies are identified, and the key success factors for the adoption of cloud computing services are analyzed based on the empirical investigation performed as part of this work. Finally, the benefits and constraints of the different cloud computing service models are presented including also the state-of-the-art research in the cloud computing area, and a summary of the most important results.