Distributed Database Management System (DDBMS) is a type of DBMS which manages a number of databases hoisted at diversified locations and interconnected through a computer network. It provides mechanisms so that the distribution remains oblivious to the users, who perceive the database as a single database. This tutorial discusses the important theories of distributed database systems. A number of illustrations and examples have been provided to aid the students to grasp the intricate concepts of DDBMS.