Resource management in distributed multimedia systems (DMS) is a central issue, due to the real-time requirements of continues media. However, in complex and mobile systems effective resource reservation becomes almost impossible. Recent research proposes adaptive applications as a complementary solution. This article reviews and generalizes issues surrounding adaptation in DMS. As a background, it first discusses heterogeneous networks and the rationale behind adaptation. Then it explains the basic common notions and mechanisms involved, followed by implementation examples. This reveals the importance of standardized system support for adaptation. The author concludes by discussing some outstanding research issues.