The term "chiral" (from the Greek for "hand") is applied to molecular systems whose asymmetry results in handedness; that is, the existence of a pair of nonsuperimposable mirror-image shapes (as illustrated by the relationship between one's right and left hands).

Lord Kelvin coined the term "chirality" in 1884, but it did not come into common usage until the 1960s. Many macroscopic examples of handed systems exist, including any object that features an inherent spiral or twist that can exhibit a left- and right-handed form: scissors, spiral staircases, screw threads, gloves, and shoes. Some mineralogical materials exhibit handedness in the solid state. In 1801 the crystallographer René observed that there were right- and left-handed quartz crystals, a phenomenon known as hemihedrism. The term "enantiomorphous" ("in opposite shape") was created to describe the macroscopic relationships between nonsuperimposable, mirror-image crystalline forms.

Chirality is a property of asymmetry important in several branches of science. The wordchiralityis derived from the Greek χειρ (kheir), "hand," a familiarchiralobject. An object or a system ischiralif it is distinguishable from its mirror image; that is, it cannot be superposed onto it.