Thyagaraya Nagar, popularly known by its abbreviated form T. Nagar, is a Shopping Paradise in the city of Chennai, Tamilnadu state, India. T. Nagar was constructed between 1923 and 1925 by the Madras Presidency government of the Raja of Panagal as a part of town planning activities initiated according to the Madras Town Planning Act of 1920. The town was named after Justice Party leader Sir P. Theagaraya Chetty. The streets, parks and localities in the new neighbourhood were named after important officials in the provincial government.

The neighbourhood is considered the biggest shopping district in India by revenue. Though conceived as a residential locality, it is now one of the principal shopping districts of the city. It is mostly famous for its plethora of Saree and gold retailers like Pothys, Nalli Silks and Saravana Stores. The neighbourhood is served by Mambalam railway station of the Chennai Suburban Railway Network. Panagal Park is located at the centre of the neighbourhood connecting Five vein-roads of the neighbourhood: North Usman Road, South Usman Road, G.N. Chetty Road, Thyagaraya Road and Venkatanarayana Road. Unofficially, T. Nagar is the Commercial Capital of the City pushing back Parrys Corner, the centre of the city. Pondy Bazaar serves as the Satellite commercial hub for T. Nagar located around the Thyagaraya Road.

T. Nagar is located about 10 km from Chennai Airport and about 8 km from Chennai Central railway station. It lies to the west of the arterial Anna Salai (Mount Road) and is loosely bordered by Saidapet to the south and southwest, West Mambalam to the west, Kodambakkam to the northwest, Nandanam to the south, Nungambakkam to the north, and Teynampet to the east. T. Nagar is usually associated with Mambalam, a common name for the entire area of T. Nagar, West Mambalam, C I T Nagar and Pondy Bazaar.

T.Nagar's bazaars are frequented by a number of shoppers. On a typical weekend, the number of people who move about on Pondy Bazaar, the suburb's principal commercial area, might soar up to 500,000. During festival season, because of the discounts and reductions offered by dealers of silk sarees and jewellers, this number might reach 2 million. Even on a lean day, about 200,000 pedestrians traverse the roads around Panagal Park, the central part of the neighbourhood.

T.Nagar is considered to be the biggest shopping district in India by revenue. There are a number of apparel, jewellery and utensil stores based in Thiyagaraya Nagar. By some estimates, the shops in the neighbourhood together account for revenues of nearly ₹ 200,000 million annually. However, official estimates put it much lower at over ₹ 100,000 million, which is still double that of New Delhi's Connaught Place and Mumbai's Linking Road which account for about ₹ 40,000 to 60,000 million annually. The neighbourhood accounts for about 70 to 80 percent of the gold sold in Chennai, the most important gold market in South India. Usman Road is the costliest commercial stretch in Chennai. The area around Panagal Park is known for its high-end textile shops, chiefly dealing with silk sarees, and jewellery stores. As of 2006, the real estate prices were ₹ 11,500 per square feet. Wardrobes stores Nalli Chinnasamy Chetti and Naidu Hall are based in Theagarya Nagar. Other important wardrobe stores such as Pothys, The Chennai Silks, RmKV and kumaran silks and also have their showrooms in Theagarya Nagar. Retail giant Saravana Stores has a wardrobe showroom and an utensils showroom in Thiyagaraya Nagar. Ranganathan Street is one of the most crowded roads for pedestrian traffic during day time. The road is full of big name establishments side-by-side smaller and petty shops (street vendors) that sell all sorts of household goods, garments & accessories, etc.,.

It also houses one of the oldest private lending libraries in the city, 'Raviraj Lending Library' on Usman Road.

T.Nagar offers a variety of entertainment options. It has grown to become a major hub for the Carnatic music festival-season, with a number of sabhas (such as Krishna Gana Sabha, Vani Mahal and Bharath Kalachar) hosting famous performers.

It also has a number of parks, cricket grounds, and other recreational facilities. The RKM cricket ground adjoining GN Chetty road hosts division IV and V city-league games.

T.Nagar residents are an unusual mix of the traditional and the modern and this is reflected in the way the neighbourhood has been growing. Several new eateries have come up while at the same time, traditional restaurants are also packed. With the city extending its bed-time more every year, the locality has acquired a reputation of always being in the fast lane. The grand textile showrooms close very late at night, and their hoarding boards constantly illuminate the roads. Early in the morning, joggers and walkers take full advantage of the empty roads, with the fresh air that's so hard to come by in this area at all other times of the day. Panagal Park, Natesan Park and Jeeva Park all have their regular crowd and their walkers' associations are extremely active. T.Nagar is also a place of musical intellects. Lot of sabhas are very active during the December month.