Mediation aims at enabling dynamic composition of multiple components by making them interact successfully in order to satisfy given requirements. Through dynamic composition, software systems can adapt their structure and behaviour in dynamic and heterogeneous environments such as ubiquitous computing environments. This paper provides a review of existing mediation approaches and their key characteristics and limitations. We claim that only a multifaceted approach that brings together and enhances the solutions of mediation from different perspectives is viable in the long term. We discuss how requirements can help identify synergies and trade-offs between these approaches and drive the selection of the appropriate mediation solution. We also highlight the open issues and future research directions in the area.