The Andaman Sea (မုတ္တမ; moʊʔtəma̰) is a body of water to the southeast of the Bay of Bengal, south of Myanmar, west of Thailand and east of the Andaman Islands; it is part of the Indian Ocean. It is roughly (north-south) and wide (east-west), with an area of . Its average depth is , and the maximum depth is .
Running in a rough north-south line on the seabed of the Andaman Sea is the boundary between two tectonic plates, the Burma plate and the Sunda Plate. These plates (or microplates) are believed to have formerly been part of the larger Eurasian Plate, but were formed when transform fault activity intensified as the Indian Plate began its substantive collision with the Eurasian continent.
As a result, a seafloor spreading centre was created, which began to form the marginal basin which would become the Andaman Sea, the current stages of which commenced approximately 3-4 million years ago (Ma).