A swather, or windrower, is a farm implement that cuts hay or small grain crops and forms them into a windrow. "Swather" is predominantly the North American term for these machines. In Australia and other parts of the world, they are called "windrowers". They aid harvesting by speeding up the process of drying the crop down to a moisture content suitable for harvesting and storage.

A swather may be self-propelled via an internal combustion engine, or may be drawn by a tractor and powered through a power take-off shaft. A swather uses a sickle bar (see mower) or cutting discs to cut the stems of the crop. A reel helps the cut crop fall neatly onto a canvas or auger conveyor which moves it and deposits it into a windrow, with all stems oriented in the same direction. Horizontal rollers behind the cutters may be used to crimp the stems of the crop to decrease drying time. The mown strip left behind is the swathe.
For hay crops, this is the same basic sequence as is also done in other ways, such as hand scything, cradling, and swathing, mowing with a mower and then raking with a hay rake, or mowing and conditioning with a mower-conditioner (the latter two sometimes also with additional tedding). With grain crops, as combines replaced threshing machines, the swather introduced a new step in the harvesting process to provide for the drying time that binding formerly afforded. Binding allowed subsequent temporary storage of the cut plants before threshing (either in stooks or in a barn), during which time they dried out.
Combine harvesting removes the binding and temporary pre-threshing storage step from the harvesting process, but in many regions of the world, combining without swathing, that is, reaping and threshing a standing plant at the same time, produces threshed grain that is too high in moisture for reliable storage. Getting around that problem drove the development in the 1920s and 30s both of swathing practice for grain crops, and, especially after World War II, of widespread industrial-scale grain drying.
Swathing (windrowing) is more common in the northern United States and Canada because the curing time for grain crops is reduced by cutting the plant stems. In regions with longer growing seasons, grain crops are usually left standing and harvested directly by combines. In the latter regions the grain can reliably reach a low-enough moisture level while still on the standing plant, whereas in regions less conducive to such drying, swathing provides the extra help needed for the grain to reach the ideal level of moisture.
Regardless of which harvesting method is used, threshed grain can receive additional drying, or not, as needed for storage; the ideal in energy efficiency, productivity, and cost-effectiveness is to get grain straight out of the combine that is dry enough. Reality does not always match that, and a damp harvest followed by drying is much better than no harvest. Farmers who do not have their own grain drying equipment will often sell to the grain elevator company to do the drying, with the expense docked from the price paid for the grain.The Swather is the mascot of sports teams at Hesston High School in Hesston, Kansas, USA. Hesston is the home to AGCO Corporation's large swather and combine harvester manufacturing plants.