Thailand is a rapidly growing country with a large middle class, and as a result may be undergoing a structural transition, changing the nature and shape of electricity demand in the coming years. Thai energy policy is driven by the three pillars of security, affordability and environmental sustainability. Concerns over fuel diversity underlie all three of these pillars and thus are a major driver of Thailand’s current long-term view of power sector development. Thailand is seeking to diversify its power sector over the next two decades by increasing coal generation and an increase in both domestic and imported renewables. In addition, Thailand is seeking to reduce the need for investment in generation and transmission by improving energy efficiency. In this study, the IEA explores the state of electricity sector development in Thailand within the framework of the IEA Electricity Security Action Plan, and provides policy recommendations to the government of Thailand on possible market design and regulatory changes to enhance the security and sustainability of its electricity system.