Haarlemmermeer (Dutch pronunciation: [ˌɦaːrlɛmərˈmeːr] ^ⓘ) is a municipality in the west of the Netherlands, in the province of North Holland. Haarlemmermeer is a polder, consisting of land reclaimed from water. The name Haarlemmermeer means 'Haarlem's lake', referring to the body of water from which the region was reclaimed in the 19th century.

Haarlemmermeer's main town is Hoofddorp, which has a population of 76,660. Hoofddorp, along with the rapidly growing towns of Nieuw-Vennep and Badhoevedorp, are part of the Randstad agglomeration. The main international airport of the Netherlands, Schiphol, is located in Haarlemmermeer.

The original Haarlemmermeer lake is said to have been mostly a peat bog, a relic of a northern arm of the Rhine which passed through the district in Roman times. In 1531, the original Haarlemmermeer had an area of 26.0 square kilometres (10.0 sq mi), and near it were three smaller lakes: the Leidsche Meer (Leiden Lake), the Spiering Meer, and the Oude Meer (Old Lake), with a combined area of about 31 square kilometres (12 sq mi).

The four lakes were formed into one by successive floods with the Haarlemmermeer name being applied to the combined lake. Villages disappeared in the process. One of those villages was Vennep, after which the modern Nieuw-Vennep was named. In Dutch, the tendency for lakes to grow over time is called the waterwolf. During the Dutch War of Independence, the waters of the Haarlemmermeer were the scene of the Battle of Haarlemmermeer, a naval engagement between a Spanish fleet and the ships of the Dutch rebels known as "Sea Beggars", who were trying to break the Siege of Haarlem.

The Haarlemmermeer could be a dangerous place during storms. On 7 January 1629, Frederick Henry of the Palatinate, son and heir of Frederick V, the "Winter King" drowned trying to cross it. By 1647, the new Haarlemmermeer had an area of about 150 square kilometres (58 sq mi), which a century later had increased to over 170 square kilometres (66 sq mi).

In 1643, Jan Adriaanszoon Leeghwater proposed to dike and drain the lake. Similar schemes, among which those of Nicolaus Samuel Cruquius in 1742 and of Baron van Lijnden van Hemmen in 1820, were proposed from time to time. But it was not until a furious hurricane in November 1836 drove the waters as far as the gates of Amsterdam, and another on Christmas Day sent them in the opposite direction to submerge the streets of Leiden, that the matter was seriously considered.

On 1 August 1837, King William I appointed a royal commission of inquiry. Their proposal receiving the sanction of the Dutch Parliament's Second Chamber in March 1839, and in the following May the work was begun.

First, a canal was dug around the lake, called Ringvaart (Ring Canal), to carry the water drainage and boat and ship traffic which had previously gone across the lake. This canal was 61 kilometres (38 mi) long, and 2.40 metres (7.9 ft) deep, and the excavated earth was used to build a dike from 30 to 50 metres (98 to 164 ft) wide around the lake. The area enclosed by the canal was more than 180 square kilometres (69 sq mi), and the average depth of the lake 4 metres (13 ft). As the water had no natural drainage, it was calculated that probably 1000 million tons of water would have to be raised by mechanical means.