Tamil Nadu /ˈtæmɨl ˈnɑːduː/ (Tamiḻ Nāṭu [t̪amɨɭ naːɖɯ] ( listen)) is one of the 28 states of India. Its capital is Chennai, the largest city. Tamil Nadu lies in the southernmost part of the Indian Peninsula and is bordered by the union territory of Pondicherry, and the states of Kerala, Karnataka, and Andhra Pradesh. It is bound by the Eastern Ghats in the north, the Nilgiri, the Anamalai Hills, and Palakkad on the west, by the Bay of Bengal in the east, the Gulf of Mannar, the Palk Strait in the south east, and by the Indian Ocean in the south.

Tamil Nadu is the eleventh largest state in India by area and the seventh most populous state. It is the fourth largest contributor (as of 2010) to India's GDP and ranks tenth in Human Development Index as of 2006. Tamil Nadu is also the most urbanised state in India. The state has the highest number (10.56%) of business enterprises and stands second in total employment (9.97%) in India, compared to the population share of about 6%.

The region has been the home of the Tamil people since at least 500 BCE. Its official language Tamil has been in use in inscriptions and literature for over 2000 years. Tamil Nadu is home to many natural resources, Hindu temples of Dravidian architecture, hill stations, beach resorts, multi-religious pilgrimage sites and eight UNESCO World Heritage Sites.