Adyar or Adayar is a large locality in south Chennai (previously Madras). It is located on the southern banks of the Adyar river. It is bounded by the Buckingham Canal to the west, Tiruvanmiyur to the south, and Besant Nagar to the east. Adyar includes various sub-localities like Indiranagar, kasturbanagar, Gandhinagar, Valmikinagar etc.

Adyar is noted for housing the Theosophical Society, which provides a calm environment along the south bank of the river for quiet contemplation on comparative religion. The Elliot's beach in nearby Besant Nagar is the nearest point to the sea, and a popular recreation spot. IIT Madras, one of the top technical institutes in India, is situated in Adyar.

The locality has developed significantly through the late 1970s and early 1980s as a residential area to accommodate Chennai's sprawl. Since the late 1990s, it has become part of the IT corridor, the name given to the part of southeast Chennai where several IT companies have set up base.