This paper discusses the sources of variability in heterogeneous and mobile networks that make it difficult for traditional applications to work properly. The problems associated with delivering multimedia content to clients of varying capabilities are also investigated. Adaptivity is presented as a tool to extend the lifetime of critical applications as well as a technique to meet client device variability. To this end we have developed prototypes for the mobile environments that aim to reduce dependency on scarce resources. The adaptation space framework is used to provide a flexible and consistent design strategy.