Prayagraj (; ISO: Prayāgarāja), formerly called Allahabad, is a metropolis in the Indian state of Uttar Pradesh. It is the administrative headquarters of the Prayagraj district, the most populous district in the state and 13th most populous district in India and the Prayagraj division. The city is the judicial capital of Uttar Pradesh with the Allahabad High Court being the highest judicial body in the state. As of 2011, Prayagraj is the seventh most populous city in the state, thirteenth in Northern India and thirty-sixth in India, with an estimated population of 1.53 million in the city. In 2011, it was ranked the world’s 40th fastest-growing city. The city, in 2016, was also ranked the third most liveable urban agglomeration in the state (after Noida and Lucknow) and sixteenth in the country. Hindi is the most widely spoken language in the city.

Prayagraj lies close to Triveni Sangam, the “three-river confluence” of the Ganges, Yamuna, and the mythical Sarasvati. It plays a central role in Hindu scriptures. The city finds its earliest reference as one of the world’s oldest known cities in Hindu texts and has been venerated as the holy city of Prayāga in the ancient Vedas. Prayagraj was also known as Kosambi in the late Vedic period, named by the Kuru rulers of Hastinapur, who developed it as their capital. Known as Purimtal in ancient Jain scriptures, it is also a sacred place for Jains, as their first Tirthankar, Rishabhdeva attained kevalya gyana here. This was one of the greatest cities in India from the late Vedic period until the end of the Maurya Empire, with occupation continuing until the Gupta Empire. Since then, the city has been a political, cultural and administrative centre of the Doab region.

Akbarnama mentions that the Mughal emperor Akbar founded a great city in Allahabad. Abd al-Qadir Badayuni and Nizamuddin Ahmad mention that Akbar laid the foundations of an imperial city there which was called Ilahabas or Ilahabad. In the early 17th century, Allahabad was a provincial capital in the Mughal Empire under the reign of Jahangir. In 1833, it became the seat of the Ceded and Conquered Provinces region before its capital was moved to Agra in 1835. Allahabad became the capital of the North-Western Provinces in 1858 and was the capital of India for a day. The city was the capital of the United Provinces from 1902 to 1920 and remained at the forefront of national importance during the struggle for Indian independence.

Prayagraj is one of the international tourism destinations, securing the second position in terms of tourist arrivals in the state after Varanasi. Located in southern Uttar Pradesh, the city covers 365 km (141 sq mi). Although the city and its surrounding area are governed by several municipalities, a large portion of Prayagraj district is governed by the Prayagraj Municipal Corporation. The city is home to colleges, research institutions and many central and state government offices, including High court of Uttar Pradesh. Prayagraj has hosted cultural and sporting events, including the Prayag Kumbh Mela and the Indira Marathon. Although the city’s economy was built on tourism, most of its income now derives from real estate and financial services.