Graphene oxide (GO) has been long-considered the most convenient route towards the large scale production of graphene. Additionally, the functional groups present within GO permit both covalent and non-covalent chemical functionalization, in particular with polymeric materials. The functionalization of GO therefore enables the development of graphene-based composite materials which possess the properties of both the matrix and the remarkable electrical, thermal and mechanical properties of both GO and graphene. In this review, we discuss the functionalization of GO in two broad settings: macromolecular functionalization of GO, and the use of GO in dispersed/colloidal systems. We review numerous methods for the functionalization of GO with initiators or chain transfer agents to permit controlled/living radical polymerization (CLRP) to take place from the surface of GO; the use of GO as a polymerization initiator, as well as non-covalent polymeric modification is discussed. For applications of GO in dispersed systems, we discuss the incorporation of GO into miniemulsions, emulsions and other dispersed phase polymerization systems, as well as techniques such as layer-by-layer assembly and colloidal templating. The use of GO as a ‘colloidal surfactant’ is also reviewed. These functionalization methods are discussed within the framework of creating materials with enhanced properties for specific applications including electrodes, capsules, polymer particles and composite films.