Patna (; Hindi: [ˈpəʈnaː] , ISO: Paṭanā), historically known as Pāṭaliputra, is the capital and largest city of the state of Bihar in India. According to the United Nations, as of 2018, Patna had a population of 2.35 million, making it the 19th largest city in India. Covering 250 square kilometres (97 sq mi) and over 2.5 million people, its urban agglomeration is the 18th largest in India. Patna also serves as the seat of Patna High Court. The Buddhist, Hindu and Jain pilgrimage centres of Vaishali, Rajgir, Nalanda, Bodh Gaya and Pawapuri are nearby and Patna City is a sacred city for Sikhs as the tenth Sikh Guru, Guru Gobind Singh was born here. The modern city of Patna is mainly on the southern bank of the river Ganges. The city also straddles the rivers Son, Gandak and Punpun. The city is approximately 35 kilometres (22 mi) in length and 16 to 18 kilometres (9.9 to 11.2 mi) wide.

One of the oldest continuously inhabited places in the world, Patna was founded in 490 BCE by the king of Magadha. Ancient Patna, known as Pataliputra, was the capital of the Magadha Empire throughout the Haryanka, Nanda, Mauryan, Shunga, Gupta, and Pala dynasties. Pataliputra was a seat of learning and fine arts. It was home to many astronomers and scholars including Aryabhata, Vātsyāyana and Chanakya. During the Maurya period (around 300 BCE) its population was about 400,000. Patna served as the seat of power, and political and cultural centre of the Indian subcontinent during the Maurya and Gupta empires. With the fall of the Gupta Empire, Patna lost its glory. The British revived it again in the 17th century as a centre of international trade. Following the partition of Bengal presidency in 1912, Patna became the capital of Bihar and Orissa Province.

Until the 19th century, it was a major trading and commercial hub in India. After independence there were a few downturns but its economy was still stable. After the separation of Jharkhand from Bihar, it lost its glory. As per the Directorate of Economics and Statistics (Government of Bihar), Nominal GDP of Patna District was estimated at INR 63,176.55 crores in 2011-12. As of 2011-12, Patna already recorded per capita gross domestic product of ₹1,08,657, way ahead of many other Indian cities and state capitals. Using figures for assumed average annual growth, Patna is the 21st fastest growing city in the world and 5th fastest growing city in India according to a study by the City Mayors Foundation. Patna registered an average annual growth of 3.72% during 2006–2010. As of 2011-12, the GDP per capita of Patna is ₹1,08,657, and its GDP growth rate is 7.29 per cent. In June 2009, the World Bank ranked Patna second in India (after Delhi) for ease of starting a business.