Tamil Nadu (; Tamil: [ˈtamiɻ ˈnaːɽɯ] (listen), abbr. TN) is the southern-most state of India. The tenth largest Indian state by area and the sixth largest by population, Tamil Nadu is the home of the Tamil people, whose Tamil language—one of the longest surviving classical languages in the world—is widely spoken in the state and serves as its official language. The capital and largest city is Chennai.

Located on the south-eastern coast of the Indian peninsula, Tamil Nadu is defined by the lush Western Ghats and the semi-arid Deccan Plateau in the west, the discontinuous Eastern Ghats in the north, the fertile Eastern Coastal Plains lining the Bay of Bengal in the east, the Gulf of Mannar and the Palk Strait to the south-east, the Laccadive Sea at the southern cape of the peninsula—Kanyakumari, and the river Kaveri bisecting the state. Politically, Tamil Nadu is bound by the Indian states of Kerala, Karnataka, and Andhra Pradesh, and the union territory of Puducherry, as well as an international maritime border with the Northern Province of Sri Lanka at Pamban Island.

Historically, Tamil Nadu had been continuously inhabited by modern humans from 15,000 BC. The at-large Tamilakam region dominated by the Tamil-speaking population was under several regimes over centuries, such as the Sangam era (300 BC–AD 300) rulers of the Chera, Chola, and Pandya clans, the Pallava dynasty (3rd–9th century), and the later Vijayanagara Empire (14th–17th century), all of which shaped the state's cuisine, culture, and architecture. European colonization began with establishing trade ports in the 17th century, with the British controlling much of South India as the Madras Presidency, an administrative province of British India. After the Indian Independence in 1947, the region became the Madras State of the Republic of India, and in 1956, the state borders were redrawn linguistically by the States Reorganisation Act (1956) into the current shape. The state was renamed as Tamil Nadu, meaning "Tamil Country", in 1969.

As the most urbanised state of India, Tamil Nadu boasts an economy with gross state domestic product (GSDP) of ₹24.85 lakh crore (US$310 billion), marking the second-largest economy amongst the 28 states of India. It has the country's 9th-highest GSDP per capita of ₹225,106 (US$2,800), and ranks 11th in human development index. Tamil Nadu is also one of the most industrialised states, with the manufacturing sector accounting for more than one-third of the state's GDP. Home to a number of ancient relics, historic buildings, religious pilgrimage spots, hill stations, forts, and three World Heritage Sites, Tamil Nadu's tourism industry is the largest among the Indian states. 15% of Tamil Nadu's forests are protected areas, hosting diverse wildlife. The Tamil film industry, nicknamed as Kollywood, plays an influential role in the state's popular culture.