Thailand's policy makers are seeking to strengthen the foundations for sustainable economic and social development. Responding to the threat of climate change, the aim includes reducing energy intensity and greenhouse gas emissions throughout the economy. Representing 35 percent of final energy use in 2010 transportation's share is slowly growing and now equals that of manufacturing. Almost totally reliant on fossil fuels, transportation is a major source of greenhouse gas emissions that contribute to climate change. The aim of this policy note is to describe in plain language what 'green transport' is, why it is important, and how it can be effectively adopted by Thai policy makers. The primary focus is on green transport options that improve welfare, mitigate excessive energy use, reduce global emissions, and air pollution. Consequently, achievement of 'green transport' to support the vision of 'green growth' requires consideration of transport's impacts across all relevant dimensions: 1) economic efficiency; 2) environmental sustainability; and 3) social sustainability. The objectives of this policy note are to: examine green transport's development challenges; provide a conceptual and policy framework for green transport; indicate the potential impacts of measures to achieve green transport; and prioritize green transport interventions. The scope is limited to land passenger and freight transport that represents almost 80 percent of total transport energy use in Thailand. Most of the balance of transport-related energy use is represented by aviation. A growing concern for environmental sustainability directs more attention to 'sustainable transport' and 'green transport'. In simple terms, the majority of transport except for walking and other non-motorized modes is not green or sustainable. Achieving green transport requires comprehensive analysis of costs and impacts. Economic, social and environmental benefits often go hand in hand. For many transport projects, maximization of 'green' impacts requires projects to deliver strong user benefits through faster and more reliable travel times to induce travel behavior changes such as mode shift that may deliver the desired 'green' benefits.