A distributed system is a collection of independent computers that appear to the users of the system as a single computer. Distributed System has its own features and the features are Resource sharing, Openness, Concurrency, Scalability, Fault Tolerance and Transparency. The Distributed System can be extended effectively in an environment using Open Systems. It is with the respect to the hardware and software. The Distributed system is scalable in effectively handling the growth of the system. A distributed database is a set of databases stored on multiple computers that typically appears to applications as a single database. Consequently, an application can simultaneously access and modify the data in several databases in a network. A distributed database system allows applications to access data from local and remote databases. The book will be very useful for the software engineers, designers, learners, and technical personals. Regardless of the immediate learning goals, the book is a handy reference and companion tool for future use. All the Concepts have been planned carefully and presented well with suitable illustrations.