The Red Fort or Lal Qila is a historic fort in the Old Delhi neighborhood of Delhi, India, that historically served as the main residence of the Mughal emperors. Emperor Shah Jahan commissioned construction of the Red Fort on 12 May 1639, when he decided to shift his capital from Agra to Delhi. Originally red and white, its design is credited to architect Ustad Ahmad Lahori, who also constructed the Taj Mahal.

The fort was plundered of its artwork and jewels during Nader Shah's invasion of the Mughal Empire in 1739. Most of the fort's marble structures were subsequently demolished by the British following the Indian Rebellion of 1857. The fort's defensive walls were largely undamaged, and the fortress was subsequently used as a garrison.

On 15 August 1947, the first Prime Minister of India, Jawaharlal Nehru, raised the Indian flag above the Lahori Gate. Every year on India's Independence Day (15 August), the prime minister hoists the Indian tricolor flag at the fort's main gate and delivers a nationally broadcast speech from its ramparts through the Public Address System of Indian Army Corps of Signals.

The Red Fort was designated a UNESCO World Heritage Site in 2007 as part of the Red Fort Complex.

The fortress-palace was a focal point of the city of Shahjahanabad, which is present-day Old Delhi. Shah Jahan's successor, Aurangzeb, added the Moti Masjid (Pearl Mosque) to the emperor's private quarters, constructing barbicans in front of the two main gates to make the entrance to the palace more circuitous.

The administrative and fiscal structure of the Mughal dynasty declined after Aurangzeb, and the 18th century saw a degeneration of the palace. In 1712 Jahandar Shah became the Mughal Emperor. Within a year of beginning his rule, Shah was murdered and replaced by Farrukhsiyar. In 1739, Persian emperor Nadir Shah easily defeated the strong Mughal army of around 200,000 soldiers, plundering the Red Fort, including the Peacock Throne.