Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula (C₂H₅)₂O. It is a colorless, highly volatile flammable liquid with a characteristic odor. It is commonly used as a solvent and was once used as a general anesthetic.

The compound may have been created by either Jābir ibn Hayyān in the 8th century or Raymundus Lullus in 1275, although there is no contemporary evidence of this. It was first synthesized in 1540 by Valerius Cordus, who called it "sweet oil of vitriol" (oleum dulce vitrioli)—the name reflects the fact that it is obtained by distilling a mixture of ethanol and sulfuric acid (then known as oil of vitriol)—and noted some of its medicinal properties. At about the same time, Theophrastus Bombastus von Hohenheim, better known as Paracelsus, discovered ether's analgesic properties in chickens. The name ether was given to the substance in 1730 by August Sigmund Frobenius.

It is particularly important as a solvent in the production of cellulose plastics such as cellulose acetate.