This chapter addresses the utilisation of geopolymers in the immobilisation of a variety of different hazardous wastes. Several elements have been investigated in detail in terms of immobilisation in geopolymers, in particular Pb and Cr as wastes from the mining industry, and Cs and Sr in radioactive wastes. There are varying degrees of effectiveness observed for different elements; geopolymer chemistry appears to provide an ideal matrix for the immobilisation of low-charged cationic species, but transition metals with the ability to take on very high oxidation states tend to be problematic. Many metallic elements appear to be trapped in the geopolymer binder in the form of precipitated hydroxides; this can give very good leach resistance in near-neutral or alkaline environments but is less desirable under acidic conditions. It is important to tailor binder chemistry to match the critical species to be immobilised; some species are much more effectively treated by immobilisation in Portland cement or alkali activated slags than in geopolymers, while in other cases the opposite is true. Waste immobilisation, in geopolymers or any other class of materials, is a highly complex area requiring detailed scientific study if acceptable and predictable results are to be obtained.