group of four polders, central Netherlands, that were reclaimed from the IJsselmeer, a lake that used to be part of the former Zuiderzee. The polders are located in the lake's southern part and along its eastern shore (except for Wieringermeer in the northwest).

The Zuiderzee project, which involved the construction of a dam (Afsluitdijk; completed 1932) enclosing the IJsselmeer and the subsequent land reclamation of its rich marine clay, began in 1920, following the plans of engineer-statesman Cornelis Lely. The Wieringermeer Polder (75 square miles 【193 square km】), the Northeast (Noordoost) Polder (181 square miles 【469 square km】), and the East (Oostelijk) Flevoland Polder (204 square miles 【528 square km】) were completed in 1930, 1942, and 1957, respectively. The South (Zuidelijk) Flevoland Polder (166 square miles 【430 square km】) was completed in 1968. A fifth potential polder is the Markerwaard Polder in southwest IJsselmeer. Under construction since 1963, its diking was partially complete by the mid-1980s, but plans were then abandoned.

The Wieringermeer Polder, on the northeastern coast of Noord-Holland, has been incorporated into that province. The Northeast, East Flevoland, and South Flevoland polders were united in 1986 into one administrative unit called Flevoland province, centring on the new town of Lelystad.

The four polders reclaimed from the IJsselmeer increased the land area of The Netherlands by about 626 square miles (1,620 square km). Originally intended almost exclusively for agricultural production (corn 【maize】, wheat, oilseeds, sugar beets, potatoes), the polders are also used for industrial and recreational purposes and as residential areas.