XY, xy, and variants may refer to:
XYY syndrome is a genetic condition in which a human male has an extra male (Y) chromosome, giving a total of 47 chromosomes instead of the more usual 46. This produces a 47,XYY karyotype, which occurs every 1 in 1,000 male births.
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 shoots and leaves, but it also transports some nutrients.
Xylitol /ˈzaɪlᵻtɒl/ is a sugar alcohol used as a sweetener. The name derives from Greek: ξύλον, xyl[on], "wood" + suffix -itol, used to denote sugar alcohols.
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.
The valley carpenter bee, Xylocopa varipuncta, is one of three species of carpenter bee found from western New Mexico to southern California.
The XYZ Affair was a political and diplomatic episode in 1797 and 1798, early in the administration of John Adams, involving a confrontation between the United States and Republican France that led to an undeclared war called the Quasi-War.