M.Sc. (Computer Science) / Concurrency control is the problem that exists in a database management system when more than one transaction or application is executed simultaneously. If transactions or applications are executed sequentially there will- be no problem with the allocation of resources. It is however necessary to execute transactions concurrently to utilise computer and resource capacity to its maximum extent. It can lead to inconsistent data if this concurrent execution of transactions are not properly controlled. If this should happen the data would be of no more use to the users of a system. The thesis is divided in the following way. Chapter 1 gives background information on the concurrency control problem. In chapter 2 a couple of mechanisms for solving the concurrency control problem are studied briefly. Chapters 3 and 4 provides a more in depth study of two specific mechanisms namely two-phase locking and timestamps. 80th of these mechanisms have already been implemented in systems to. solve the concurrency control problem.- In chapter 5 a comparison is made of the two methods described in chapters 3 and 4. A third method for handling concurrency control is briefly described in chapter 6. This method hasn't received a lot of attention from researchers yet. And in the last chapter, chapter 7, the concurrency control method used in the SDD-1 system is studied in more detail. SDD-1 is a distributed database management system.