Lasne (Walloon: Lane) is a Walloon municipality in the Belgian province of Walloon Brabant, south east of Brussels. In 2008, Lasne had a population of 14,043. The total area is 47.22 km² which gives a population density of 297 inhabitants per km². Lasne is the richest municipality in Wallonia, measured by the average taxable income of the inhabitants. It also has the lowest local taxes of any municipality in Belgium.
It was formed from the fusion of five municipalities: