Not many years ago, some researcher created the vision of the �data utility� as a key enabler towards ubiquitous and pervasive computing. As for the water and power grid, there should be a utility infrastructure, designed for worldwide availability, providing continuous access to persistent information. Such utility service should provide appropriate guarantees in terms of security, data availability and survivability, and performance independent of location from which it is accessed. Decentralization and replication would be the approach to make it resistant against security attacks. Several projects have explored (and still are exploring) the feasibility of the vision, each having a different emphasis on individual features such as data durability, uniform geographic access, privacy and support for uncensorship, mobility support, or other. Applications which benefit from such global data service would be many, ranging from distributed, Internet-wide file services, to mobile data provisioning, content distribution, data backup, digital libraries and information retrieval. Similarly, information systems for national security, world-wide safety infrastructures and other systems which rely on sensors (physical or logical e.g. firewalls, packet filters), all require a decentralized, inter-organizational data collection and processing infrastructure, able to process in real time a huge amount of data, and filter, correlate and securely distribute information to many users. This book aims at presenting an organic view on the research and technologies that are bringing us towards the realization of the vision.