Laguna de Bay is the largest lake in the Philippines. It is located on the island of Luzon between the provinces of Laguna to the south and Rizal to the north. Metro Manila lies on its western shore. Its surface area is 949 square kilometers and has an average depth of only about 2 meters.

The lake is shaped like a stylized 'W', with two peninsulas jutting out from the northern shore. Talim Island is the largest island on the lake. Laguna de Bay drains to Manila Bay through the Pasig River.

Laguna de Bay is named for the municipality of Bay (Bai) in Laguna province.

The Laguna Lake Development Authority, established in 1970, is the government body responsible for promoting development and conservation works in the lake and its catchment basin.