Ductility is a technological property of matter that indicates the ability of a body or material to deform plastically under load before breaking, which may be expressed as percent elongation or percent area reduction from a tensile test — for example, the ability to withstand plastic deformations. A body is much more ductile, the higher the achieved deformation before breaking.

Ductility can also be defined as the ability of a material to be reduced in thin threads (while similarly, malleability is the ability of a material to be reduced in thin sheets). The two characteristics can be co-present having some factors in common, but this is not necessary, gold is both ductile and malleable, lead is malleable but not very ductile. The materials that most have this property are metals. Property opposed to ductility is fragility, or the inability to deform under load, thus resulting in sudden rupture (also called brittle failure).