Reliance Industries Limited is an Indian multinational conglomerate headquartered in Mumbai. Its businesses include energy, petrochemicals, natural gas, retail, entertainment, telecommunications, mass media, and textiles. Reliance is the largest public company in India by market capitalisation and revenue, and the 86th largest company worldwide. It is India's largest private tax payer and largest exporter, accounting for 7% of India's total merchandise exports.

The company has attracted controversy for reports of political corruption, cronyism, fraud, financial manipulation, and exploitation of its customers, Indian citizens, and natural resources. Its chairman, Mukesh Ambani, has been described as a plutocrat.

Reliance Commercial Corporation was set up in 1958 by Dhirubhai Ambani as a small venture firm trading commodities, especially spices and polyester yarn. In 1965, the partnership ended and Dhirubhai continued the polyester business of the firm. In 1966, Reliance Textiles Industries Pvt. Ltd. was incorporated in Maharashtra. It established a synthetic fabrics mill in the same year at Naroda in Gujarat. On 8 May 1973, it became Reliance Textiles Industries Limited. In 1975, the company expanded its business into textiles, with "Vimal" becoming its major brand in later years. The company held its initial public offering (IPO) in 1977. The issue was over-subscribed by seven times. In 1979, a textiles company Sidhpur Mills was amalgamated with the company. In 1980, the company expanded its polyester yarn business by setting up a Polyester Filament Yarn Plant in Patalganga, Raigad, Maharashtra with financial and technical collaboration with E. I. du Pont de Nemours & Co., U.S.

In 1985, the name of the company was changed from Reliance Textiles Industries Ltd. to Reliance Industries Ltd. During 1985 to 1992, the company expanded its installed capacity for producing polyester yarn by over 145,000 tonnes per annum.

The Hazira petrochemical plant was commissioned in 1991–92.

In 1993, Reliance turned to the overseas capital markets for funds through a global depository issue of Reliance Petroleum. In 1996, it became the first private sector company in India to be rated by international credit rating agencies. S&P rated Reliance "BB+, stable outlook, constrained by the sovereign ceiling". Moody's rated "Baa3, Investment grade, constrained by the sovereign ceiling".

In 1995/96, the company entered the telecommunications industry through a joint venture with NYNEX, USA, and promoted Reliance Telecom Private Limited in India.

In 1998, Reliance took over Indian Petrochemicals Corporation Limited during privatization of public sector enterprises.