Southeast Asia consists of two geographic regions: the Asian mainland (Indochina) and island arcs and archipelagoes to the east and southeast (Malay Archipelago). The mainland section consists of Burma, Cambodia, Laos, Thailand, Vietnam and Peninsular Malaysia while the maritime section consists of Brunei, East Malaysia, East Timor, Indonesia, the Philippines, and Singapore. Papua New Guinea is an observer in the Association of Southeast Asian Nations, as is East Timor.

The Andaman and Nicobar Islands of India are geographically considered part of Southeast Asia. Bangladesh and the Seven Sister States of India are culturally part of Southeast Asia and sometimes considered both South Asian and Southeast Asian. The Seven Sister States of India are also geographically part of southeast Asia. Hainan Island and several other southern Chinese regions such as Yunnan, Guizhou and Guangxi are considered both East Asian and Southeast Asian. The rest of New Guinea is sometimes included so are Palau, Guam, and the Northern Mariana Islands, which were all part of the Spanish East Indies.

Southeast Asia is rich in wildlife with animals such as orangutans, leopards, elephants, water buffalo and rhinos. There is also significant diversity in culture, language, and religion. Much of Southeast Asia is rainforest and the climate is very wet. The wet weather makes the area prime for rice patty agriculture making rice the main staple in the Southeast Asian diet.