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. The benefits of demand-side management and energy efficiency program implementation in the commercial and industrial sectors of Thailand are analyzed. Corresponding implications for power generation expansion planning and emissions are considered. Evaluation of an energy efficiency scenario reveals an energy saving of 7917 kilotons of oil equivalent in 2020, or 8.6% of total energy demand, relative to the base case. The efficiency scenario also projects electricity savings of 24,682 and 16,129 Gwh for the commercial and industrial sectors, respectively. The energy efficiency case also reduces power generation by 46,784 GWh and postpones total additional capacity of 9200 MW in 2020.