Concurrency control and deadlock detection are the most important problem that must have a powerful attention when sharing information in distributed systems. The main objective of this book is to address the deadlock detection in distributed systems, to study the performance of various deadlock detection algorithms, and to introduce an algorithm to detect deadlock with a reduction of the communication overhead through the network during the sharing of data. the book introduces the parallel deadlock detection algorithm (PDDA). This algorithm has more advantages than all previous algorithms, it detects deadlock in very good and easy manner depending on matrix representation, a simulation model is developed to study the performance of PDDA and two algorithms. One of them is selected from centralized algorithms (One-Phase Deadlock Detection Protocol) and the other one is selected from distributed algorithms (Obermarck's algorithm). In this model, the communication overhead and time delay is determined for these algorithms. The book also propose a deadlock avoidance algorithm (PDAA) this algorithm is a modification of parallel deadlock detection algorithm (PDDA).