Tamil Brahmins are Tamil-speaking Brahmins, primarily living in Tamil Nadu, although a few of them have settled in other states like, Telangana, Andhra Pradesh, Kerala and Karnataka . They can be broadly divided into three religious groups, Gurukkals who follow Saivism, Iyers who follow the Srauta and Smartha tradition and Iyengars who follow Sri Vaishnavism.
Tamil Brahmins are divided into three groups -- Iyers, Iyengars and Gurukkal. Iyers form the majority of the Tamil Brahmin population and are Smarthas, while Iyengars are Vaishnavas and Gurukkals are Saivas.
Iyers are Srauta-Smartha Brahmins, most of whom follow the Advaita philosophy propounded by Adi Shankara. Advaita Vedanta has been in existence from way before Adi Sankara. In fact, Vedanta refers to itself as Anadi, meaning without beginning and are concentrated mainly along the Cauvery Delta districts of Nagapattinam, Thanjavur, Tiruvarur and Tiruchirapalli where they form almost 10% of the total population. However the largest population reside in Nagercoil, making up to 13% of the city's population They are also found in significant numbers in Chennai, Coimbatore, Madurai, Tirunelveli, Ambasamudram, Palakkad and Trivandrum.
Iyengars follow the Visishtadvaita philosophy propounded by Sri Vikanasa or Sri Ramanujacharya. They are divided into two sub-sects: Vadakalai (Northern branch) and Thenkalai (Southern branch). They are devout worshippers of Lord Vishnu.
The sect of Sivāchārya or Gurukkal form the hereditary priesthood or in the Siva and Sakthi temples in Tamil Nadu. They are Saivites and adhere to the philosophy of Shaiva Siddhanta. They are well versed in Vedas, Agama Sasthras and follow the Agamic rituals of these temples. Because of these cultural differences, intermarriages with other Tamil Brahmanas are rare even to this date. Gurukkals are sub-divided into Tiruvalangad, Conjeevaram and Thirukkazhukunram.