Manila Bay is a natural harbor which serves the Port of Manila (on Luzon), in the Philippines. The bay is considered to be one of the best natural harbors in Southeast Asia and one of the finest in the world. It has an area of 1,994 km (769.9 sq mi), and a coastline of 190 km (118.1 mi). The entrance is 19 km (11.8 mi) wide and expands to a width of 48 km (29.8 mi). Corregidor Island divides the entrance into two channels, about 2 miles (3.2 km) towards the North and 6.5 miles (10.5 km) wide on the South side. Mariveles, in the province of Bataan, is an anchorage just inside the northern entrance and Sangley Point is the former location of Cavite Naval Base.

On either side of the bay are volcanic peaks topped with tropical foliage: 40 km to the north is the Bataan Peninsula and to the south is the province of Cavite.

Across the entrance to Manila Bay are several islands. The largest is Corregidor, which is 3 kilometers from Bataan and, along with the island of Caballo, separates the mouth of the bay into the North and South Channels. In the south channel is El Fraile Island and outside the entrance, and to the south, is Carabao Island. El Fraile, a rocky island some 4 acres (1.6 ha) in area, supports the massive concrete and steel ruins of Fort Drum, an island fortress constructed by the United States Army to defend the southern entrance of the bay. To the immediate north and south are additional harbors.

The bay was the setting for the Battle of Manila Bay in 1898 and the siege of Corregidor Island by invading Japanese forces in 1942.

Manila Bay drains approximately 17,000 km (6,563.7 sq mi) of watershed area, with the Pampanga River contributing about 49% of the freshwater influx. With an average depth of 17 m (55.8 ft), it is estimated to have a total volume of 28.9 billion cubic meters (28.9 cubic km). Today, Manila Bay still remains important for commerce and industry, including fishing, although rapid urban growth and industrialization are contributing to a decline in water quality and deteriorating marine habitats. It also serves a focus for recreation for Metro Manila and is a popular destination for walks and for viewing the sunset. Much of the land fronting the bay along Metro Manila is reclaimed land which now includes important sites such as the Philippine Senate and the Mall of Asia.