Delhi, known locally as Dilli (Hindi: दिल्ली, Punjabi: ਦਿੱਲੀ, Urdu: دلّی dillī), and also by the official name National Capital Territory of Delhi (NCT), is the second-largest metropolis in India. With over 15.9 million residents, it is the eighth largest metropolis in the world by population. The name Delhi is often also used to include some urban areas near the NCT, as well as to refer to New Delhi, the capital of India, which lies within the NCT. The NCT is a federally administered union territory. Delhi also houses Asia’s largest planned residential colony, Dwarka Sub City.

Located on the banks of the River Yamuna, Delhi has been continuously inhabited since at least the 6th century BC. After the rise of the Delhi Sultanate, Delhi emerged as a major political, cultural and commercial city along the trade routes between northwest India and the Indo-Gangetic plains. It is the site of many ancient and medieval monuments, archaeological sites and remains. In 1639, Mughal emperor Shahjahan built a new walled city in Delhi which served as the capital of the Mughal Empire from 1649 to 1857.

After the British East India Company gained control of much of India during the 18th and 19th centuries, Calcutta became the capital both under Company rule and under the British Raj, until George V announced in 1911 that it was to move back to Delhi. A new capital city, New Delhi, was built to the south of the old city during the 1920s. When India gained independence from British rule in 1947, New Delhi was declared its capital and seat of government. As such, New Delhi houses important offices of the federal government, including the Parliament of India.

Owing to the migration of people from across the country, Delhi has grown to be a cosmopolitan metropolis. Its rapid development and urbanisation, coupled with the relatively high average income of its population, has transformed Delhi. Today Delhi is a major cultural, political, and commercial center of India.