The Greater Mekong Subregion (GMS) is a natural economic area bound together by the Mekong River, covering 2.6 million square kilometers and a combined population of around 326 million.

The GMS countries are Cambodia, the People's Republic of China (PRC, specifically Yunnan Province and Guangxi Zhuang Autonomous Region), Lao People's Democratic Republic (Lao PDR), Myanmar, Thailand, and Viet Nam.

In 1992, with assistance from ADB, the six countries entered into a program of subregional economic cooperation, designed to enhance economic relations among the countries.

With support from ADB and other donors, the GMS Program helps the implementation of high priority subregional projects in transport, energy, telecommunications, environment, human resource development, tourism, trade, private sector investment, and agriculture.

Substantial progress has been achieved in terms of implementing GMS projects since 1992. Priority infrastructure projects worth around $11 billion have either been completed or are being implemented. Among these are the upgrading of the Phnom Penh (Cambodia)-Ho Chi Minh City (Viet Nam) highway and the East-West Economic Corridor that will eventually extend from the Andaman Sea to Da Nang.

The subregion embraces flora and fauna that have expanded northward along the Malay Peninsula into Thailand, encroached upon the high mountains from the Himalayas, or advanced along the broad river valleys as dry deciduous forests similar to those of India. Ten million years of changing sea levels have left a rich legacy of unique life forms that have evolved in isolation on the Cardamom and Annamite mountains of Cambodia, Lao PDR, Thailand, and Viet Nam.

These resources provide both income and sustenance to the great majority of people in the subregion who are leading subsistence or near subsistence agricultural lifestyles. The land yields timber, minerals, coal, and petroleum, while water from the many rivers supports agriculture and fisheries and provides energy in the form of hydropower. The coal reserves of the subregion are abundant, and the oil and gas reserves considerable. Most of these are in Myanmar, Thailand and Viet Nam. These abundant energy resources are still relatively underused.

Increasingly, modernization and industrialization are emerging from a process of transition and transformation. The Mekong countries are gradually shifting from subsistence farming to more diversified economies, and to more open, market-based systems. In parallel with this are the growing commercial relations among the six Mekong countries, notably in terms of cross-border trade, investment, and labor mobility. Moreover, natural resources, particularly hydropower, are beginning to be developed and utilized on a subregional basis.

The rich human and natural resource endowments of the Mekong region have made it a new frontier of Asian economic growth. Indeed, the Mekong region has the potential to be one of the world's fastest growing areas.