A windcatcher, wind tower, or wind scoop (Persian: بادگیر) is a traditional architectural element used to create cross ventilation and passive cooling in buildings. Windcatchers come in various designs, depending on whether local prevailing winds are unidirectional, bidirectional, or multidirectional, on how they change with altitude, on the daily temperature cycle, on humidity, and on how much dust needs to be removed. Despite the name, windcatchers can also function without wind.

Neglected by modern architects in the latter half of the 20th century, the early 21st century saw them used again to increase ventilation and cut power demand for air-conditioning. Generally, the cost of construction for a windcatcher-ventilated building is less than that of a similar building with conventional heating, ventilation, and air conditioning (HVAC) systems. The maintenance costs are also lower. Unlike powered air-conditioning and fans, windcatchers are silent and continue to function when the electrical grid power fails (a particular concern in places where grid power is unreliable or expensive).

Windcatchers rely on local weather and microclimate conditions, and not all techniques will work everywhere; local factors must be taken into account in design. Windcatchers of varying designs are widely used in North Africa, West Asia, and India. A simple, widespread idea, there is evidence that windcatchers have been in use for many millennia, and no clear evidence that they were not used into prehistory. The "place of invention" of windcatchers is thus intensely disputed; Egypt, Iran, and the United Arab Emirates all claim it.

Windcatchers vary dramatically in shape, including height, cross-sectional area, and internal sub-divisions and filters.

Windcatching has gained some ground in Western architecture, and there are several commercial products using the name windcatcher. Some modern windcatchers use sensor-controlled moving parts or even solar-powered fans to make semi-passive ventilation and semi-passive cooling systems.

Windscoops have long been used on ships, for example in the form of a dorade box. Windcatchers have also been used experimentally to cool outdoor areas in cities, with mixed results; traditional methods include narrow, walled spaces, parks and winding streets, which act as cold-air reservoirs, and takhtabush-like arrangements (see sections on night flushing and convection, below).

The construction of a windcatcher depends on the prevailing wind direction at that specific location: if the wind tends to blow from only one side, it may have only one opening, and no internal partitions. In areas with more variable wind directions, there may also be radial internal walls, which divide the windtower into vertical sections. These sections are like parallel chimneys, but with openings to the side, pointing in multiple directions. More sections reduce the flow rate, but increase the efficiency at suboptimal wind angles. If the wind hits the opening square-on, it will go in, but if it hits it at a sufficiently oblique angle, it will tend to slip around the tower, instead.

Windcatchers in areas with stronger winds will have smaller total cross-sections, and areas with very hot wind may have many smaller shafts in order to cool the incoming air. Windtowers with square horizontal cross-sections are more efficient than round ones, as the sharp angles make the flow less laminar, encouraging flow separation; suitable shaping increases suction.