XY, xy, and variants may refer to:
XYY syndrome is a genetic condition in which a male has an extra Y chromosome. Symptoms are usually few.
Xylem is one of the two types of transport tissue in vascular plants, phloem being the other. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients.
The xylophone (from the Greek words ξύλον—xylon, "wood" + φωνή—phōnē, "sound, voice", meaning "wooden sound") is a musical instrument in the percussion family that consists of wooden bars struck by mallets.
Xylene (from Greek ξύλο, xylo, "wood"), xylol or dimethylbenzene is any one of three isomers of dimethylbenzene, or a combination thereof.
Xylocopa varipuncta, the valley carpenter bee, is one of three species of carpenter bee found from western New Mexico to northern California.
The XYZ Affair was a political and diplomatic episode in 1797 and 1798, early in the presidency of John Adams, involving a confrontation between the United States and Republican France that led to the Quasi-War.
Xylella fastidiosa is an aerobic, Gram-negative bacterium of the monophyletic genus Xylella. It is a plant pathogen, and is transmitted exclusively by xylem fluid feeding sap insects.