An assessment of benefits of the implementation of demand-side management (DSM) and energy efficiency programs to the commercial and industrial sectors in Thailand is presented, and the corresponding impacts on power-generation expansion planning and emissions are discussed. The reference building models were simulated to capture energy consumption patterns of the medium and large commercial buildings in Thailand. Nine subsectors in the industrial sector, classified according to the international standard codes, are modeled and analyzed through the technoeconomic approach. Scenarios of the energy efficiency programs in Thailand are applied to the commercial and industrial sectors to investigate the potential of energy savings. Control technologies of airborne emissions from the utilization of fossil fuels in the power sector are also applied. Finally, a least-cost electricity expansion model is used to generate new generation plans. Features of the resultant plans include a significant reduction in the required power capacity addition and airborne emissions of fossil-fired power plants compared to a reference plan.