The Zuiderzee Works is a system of dams and dikes, land reclamation and water drainage work, which was the largest hydraulic engineering project undertaken by the Netherlands during the twentieth century. The project involved the damming of the Zuiderzee, a large, shallow inlet of the North Sea, and the reclamation of land in the newly enclosed water using polders. Its main purposes are to improve flood protection and create additional land for agriculture.

The Zuiderzee or Zuider Zee was a shallow bay of the North Sea in the northwest of the Netherlands, extending about 100 km inland and at most 50 km wide, with an overall depth of about 4 to 5 metres (13–16 feet) and a coastline of about 300 km. It covered 5,000 km2 (1,900 sq mi). Its name is Dutch for "southern sea", indicating that the name originates in Friesland, to the north of the Zuiderzee.