Iyer (also spelt as Ayyar, Aiyar, Ayer or Aiyer) is a caste of Hindu Brahmin communities of Tamil origin. Most Iyers are followers of the Advaita philosophy propounded by Adi Shankara. The majority reside in Tamil Nadu, India. Iyers are sub-divided into various sub-sects based on cultural and regional differences. Like all Brahmins, they are also classified based on their gotra, or patrilineal descent, and the Veda they follow. Apart from the prevalent practice of using the title "Iyer" as surname, Iyers also use other surnames, such as Sāstri or Bhattar.