Delhi ( , transl: dehlī), known locally as Dilli ( , , transl: dillī), and also as the National Capital Territory of Delhi (NCT), is the second-largest metropolis in India. With over 17.3 million residents, it is the sixth largest metropolis in the world by population. The name Delhi is also used to include some urban areas outside 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.

Located on the banks of the River Yamuna, Delhi has been continuously inhabited since at least the 6th century BC, according to archaeological evidence. 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.

Etymology

The etymology of "Delhi" is uncertain but many possibilities exist. The most common view is that its eponym is Dhillu or Dilu, a king of the Mauryan dynasty, who built the city in 50 BC and named it after himself. The Hindi/Prakrit word dhili ("loose") was used by the Tuar Rajputs to refer to the city because the Iron Pillar built by Raja Dhava had a weak foundation and was replaced. The coins in circulation in the region under the Rajputs were called dehliwal. Some other historians believe that the name is derived from Dilli, a corruption of dehleez or dehali—Hindi for 'threshold'—and symbolic of city as a gateway to the Indo-Gangetic Plains. Another theory suggests that the city's original name was Dhillika.