In this tutorial, I will review some of the work done in the distributed systems community on database replication, focusing on group communication–based protocols. Designing database replication systems and algorithms based on group communication leads to modular approaches, in which synchronization among servers, for example, is encapsulated in the group communication primitives. As a result, reasoning about the correctness of such systems is simpler. In addition to discussing group communication–based database replication, the tutorial is intended to illustrate the use of group communication in the design of fault tolerant distributed systems and fault–tolerant database systems.