Environmentally related taxes are seldom used in isolation to address a particular environmental problem. Most often they are used in combination with one or more other instrument categories, like direct regulations, subsidies, labelling systems, negotiated agreements, etc. OECD has for some time been studying the impacts on environmental effectiveness and economic efficiency of the fact that such instrument mixes are employed – instead of only one instrument being used per target set. Central to the work is how the different instruments interact in practice. This chapter presents some examples of instrument mixes used and highlights some of the main findings made in this work.