The Masjid-i Jahān-Numā commonly known as the Jama Masjid of Delhi, is the principal mosque of Old Delhi in India. Commissioned by the Mughal Emperor Shah Jahan, builder of the Taj Mahal, and completed in the year 1656 AD, it is the largest and best-known mosque in India. It lies at the origin of a very busy central street of Old Delhi, Chandni Chowk.

The courtyard of the mosque can be reached from the east, north and south by three flights of steps, all built of red sandstone. The northern gate of the mosque has 39 steps. The southern side of the mosque has 33 steps. The eastern gate of the mosque was the royal entrance and it has 35 steps. These steps used to house food stalls, shops and street entertainers. In the evening, the eastern side of the mosque used to be converted into a bazaar for poultry and birds in general. Prior to the 1857 War of Indian Independence, there was a madrassah near the southern side of the mosque, which was pulled down after the mutiny.

The mosque faces west. Its three sides are covered with open arched colonnades, each having a lofty tower-like gateway in the centre. The mosque is about 261 feet (80 m) long and 90 feet (27 m) wide, and its roof is covered with three domes with alternate stripes of black and white marble, with its topmost parts covered with gold. Two lofty minarets, 130 feet (41 m) high, and containing 130 steps, longitudinally striped with white marble and red sandstone, flank the domes on either side. The minarets are divided by three projecting galleries and are surmounted by open twelve-sided domed pavilions. On the back of the mosque, there are four small minarets crowned like those in the front.
The dome of the Jama Masjid.

Under the domes of the mosque, is a hall with seven arched entrances facing the west and the walls of the mosque, up to the height of the waist, are covered with marble. Beyond this is a prayer hall, which is about 61 meters X 27.5 meters, with eleven arched entrances, of which the centre arch is wide and lofty, and in the form of a massive gateway, with slim minarets in each corner, with the usual octagonal pavilion surmounting it. Over these arched entrances there are tablets of white marble, four feet (1.2 m) long and 2.5 feet (760 mm) wide, inlaid with inscriptions in black marble. These inscriptions give the history of the building of the mosque, and glorify the reign and virtues of Shah Jahan. The slab over the centre arch contains simply the words "The Guide!"

The mosque stands on a platform of about five feet (1.5 m) from the pavement of the terrace, and three flight of steps lead to the interior of the mosque from the east, north, and the south. The floor of the mosque is covered with white and black marble ornamented to imitate the Muslim prayer mat; a thin black marble border is marked for the worshippers, which is three feet long and 1 ½ feet wide. In total there are 899 such spaces marked in the floor of the mosque. The back of the mosque is cased over to the height of the rock on which the mosque stands with large hewn stones.