A description is given of Clouds, an operating system designed to run on a set of general-purpose computers that are connected via a medium-to-high-speed local area network. The structure of Clouds promotes transparency, support for advanced programming paradigms, and integration of resource management, as well as a fair degree of autonomy at each site. The system structuring paradigm chosen for Clouds is an object/thread model. All instances of services, programs, and data in Clouds are encapsulated in objects. The concept of persistent objects does away with the need for file systems, replacing it with a more powerful concept, namely, the object system. The facilities in Clouds include integration of resources by location transparency; support for various types of atomic operations, including conventional transactions; advanced support for achieving fault tolerance; and provisions for dynamic reconfiguration.