Willows have an extremely long history for medicinal uses, being used to treat fevers, aches, skin conditions, and headaches, and as an anti-clotting agent. The basic ingredient of aspirin, salicylic acid, originally came from willow bark (the chemical name comes from salix, the Latin word for willow). In the middle 1800s, scientists first synthesized acetylsalicylic acid, a biochemical derivative of salicylic acid. Then, a few years before 1900, the German company Bayer developed this compound as a commercial pain reliever, naming it "aspirin," which was the world's first mass-marketed drug. It remains one of the most-used medicines in the world.
Salicylic acid is also used in acne, psoriasis, wart, and callous treatments, and also in some dandruff shampoos and toothpastes.
When you think of the tremendous medicinal value of these plants, you must acknowledge that there may be many more important drugs "hidden" in plants that medical science simply has not yet discovered. This is one reason we must protect and conserve ecosystems and species worldwide.
Some willows have usable lumber, which tends to be rather soft but resistant to warping and splitting. Willow wood has been used for packing crates, palettes, furniture, cricket bats, and paper pulp.
Willow has been used for basketry.
Misbehaving children, in the past, were often disciplined by application of a willow switch.
Willows are planted to prevent erosion, as wind breaks, for bioremediation, and reclamation of severely impacted sites such as mines and quarries.
Many willows have ornamental value, but their fast growth causes weak, brittle wood. Their roots are notorious for invading sewer lines. Some willows are prone to diseases, too, so do some research before planting, and think carefully about placement.
In old-time Ozark dialect, the phrase "keep close to the willows" meant "to be conventional, conservative, or modest"; it apparently came from the habit of skinnydippers staying close to the trees to avoid being seen by passersby.