For cities that want to take concreteactions on improving energy efficiency, it is essential tounderstand what, where, and how big the potentialenergy-saving opportunities are, what measures are needed tocapture the savings and at what costs, what theimplementation constraints are, and how priorities should beset given local capacity and resources. An energy efficiencyassessment can provide the necessary clarity on theseissues. Energy efficiency assessments can be done atdifferent depths and with varying scopes, depending on thecity's needs, capacity, and resources. The duration andcost of the assessment depends on the quality of existingdata and the size and complexity of the sector. Thisguidance note provides an introduction to the objectives,scope, and outputs, as well as the basic steps andapproaches of conducting the three types of energyefficiency assessments.