Association of Southeast Asian Nations (ASEAN) is a regional cooperation mechanism relating to economics, sociaties, politics, securities and cultures of the 10 Southeast Asian countries.
The total population of the region is more than 620 million in 2014; it is larger than that of the European Union (EU) with a population of 500 million people in 2014, and the population growth rate is also higher than that of EU. In addition, the proportion of young generation is also very high, its consumption expansion is expected in the future. The sum of the GDP of the member states in 2013 is 2 trillion 410 billion US dollars, which is about half the size of Japan's GDP. If you look at the ASEAN as one nation, it will have the scale of the world's seventh.
December 31, 2015, the ASEAN Economic Community (AEC) was established, and started the start-up. It mainly aims at economic cooperation between ASEAN countries. Goods tariffs of more than 90% goods in the region have already been zero; it's trying to encourage high-level liberalization. Besides, it targets the liberalization and activation of the movement of such as money, people, and services in the region, and the economic development of all of the member states.

(Source) wikipedia
Name Association of Southeast Asian Nations
Land Area 4,479,210.5 square kilometer
Population 601,000,000 (in 2010)
Member States Indonesia, Cambodia, Singapore, Thailand, the Philippines, Brunei, Vietnam, Malaysia, Myanmar, Laos (10 countries)
Common Language English
Headquarters Jakarta
GDP 2,410 billion dollars (in 2013)
(Source) wikipedia and the website of Ministry of Foreign Affairs