Today's business environment has an increasing need for distributed database and client/server applications as the desire for reliable, scalable and accessible information is steadily rising. Distributed database systems provide an improvement on communication and data processing due to its data distribution throughout different network sites. Not only is data access faster, but a single-point of failure is less likely to occur, and it provides local control of data for users. However, there is some complexity when attempting to manage and control distributed database systems. In this paper, the authors describe distributed database system and their issues. A major issue of distributed database is concurrency control problem and security. So, they are also describing concurrency control problem and different concurrency control technique.