This book focuses on the economic aspects of cloud computing, a critical ICT infrastructure in our digital age. The market for cloud computing is rapidly expanding and changing the nature of business in all industries. This book estimates and analyzes the impact of the diffusion of cloud computing on the Japanese macroeconomy, employing model-based simulations. Cloud computing services are being provided not only as simple data storage services but also as various value-added services. The market has shifted to an oligopoly, with a limited number of big-name global firms as the main players. This book quantitatively estimates the impact of this shift on Japan’s utility-based social welfare. The book also discusses public policy measures that can enhance free competition in a cloud computing market with oligopolistic characteristics. One aim of this book is to provide policymakers and researchers with fundamental data and an analytic approach that can be used to formulate public policy around cloud computing in terms of both regulation and market promotion.