Climate change, energy price spikes, and concerns about energy security have reignited interest in state and local efforts to promote end-use energy efficiency, customer-sited renewable energy, and energy conservation. Government agencies and utilities have historically designed and administered such demand-side measures, but innovative third-party administrative models present new options to finance, market, and deliver sustainable energy services to energy end-users. This study outlines the concept of a new third-party administrative model, a sustainable energy utility (SEU), with the potential to achieve deep energy efficiency savings and a high penetration of customer-sited renewable energy. An SEU is characterized by central coordination, comprehensive programs, flexible incentives, financial self-sufficiency, competitive procurement, and a focus on delivering energy services rather than commodity energy. (Contains 2 tables and 7 notes.)