The summary reviews the Energy SectorManagement Assistance Programme (ESMAP) activities in energyefficiency (EE), from 1997 to 2002, and evaluates thematicimpacts, and lessons of the ESMAP Energy EfficiencyPortfolio, though outputs such as capacity and knowledge,and other downstream activities, capturing best practicesfrom lessons learned. It describes the overall impacts ESMAPplayed in mainstreaming EE within the Bank, and clientcountries, the catalytic role in supporting EE work, and itsshift from its conventional demand-side management approach,to innovative energy service-driven, institutional andfinancing delivery mechanisms. Lessons suggest a carefultopical selection for effective cross-country exchange,followed by systematic planning; establishing aninstitutional infrastructure for making energy conservationa profitable commercial business; establishing financingintermediaries between project developers and financiers, tobridge knowledge, and perception gaps, reducing transactioncosts; and, expanding knowledge dissemination on innovativemechanisms, methodologies, and strategies in project design.