This volume contains the proceedings of the 4th International Workshop on Distributed Algorithms, held near Bari, Italy, September 24-26, 1990. The workshop was a forum for researchers, students and other interested persons to discuss recent results and trends in the design and analysis of distributed algorithms for communication networks and decentralized systems. The volume includes all 28 papers presented at the workshop, covering current research in such aspects of distributed algorithm design as distributed combinatorial algorithms, distributed algorithms on graphs, distributed algorithms for new types of decentralized systems, distributed data structures, synchronization and load-balancing, distributed algorithms for control and communication, design and verification of network protocols, routing algorithms, fail-safe and fault-tolerant distributed algorithms, distributed database techniques, algorithms for transaction management and replica control, and other related topics.