The goal of increasing the energy efficiency of products, buildings and processes has been at the heart of national and international policies from the 1970s onwards. Running against conventional wisdom, this chapter highlights the limitations and the potentially counterproductive side effects of an unthinking pursuit of energy efficiency, whether alone or as part of a broader ‘whole systems’ approach. Two main critiques of energy efficiency are considered. The first focuses on the problem of ‘rebound’, the second on interpretations of normality and service that are unavoidably embedded in measures of efficiency and in related policies. If energy efficiency is to be part of the solution rather than part of the problem, questions about sufficiency need to come first: What is energy used for? How much energy do societies ‘need’? How much consumption is compatible with meeting carbon targets?.