Elasticity, the property of a substance that enables it to recover its original shape and size after it has been stretched, squeezed, or bent. All substances are elastic in one way or another.

Gases and liquids have elasticity of volume. They have the ability to expand to their original volume after a compressive force has been removed. They also expand or contract to their original volume after being heated or cooled.

Solids have elasticity of form. They tend to resume their original shapes after being deformed by bending, twisting, pulling, or pressure. Some solids, such as putty and modeling clay, are plastic, or relatively inelastic. Others, such as rubber and steel, are very elastic. All solids can be deformed beyond their elastic limit—the point at which they will no longer resume their original form, even if the deforming force is removed.

Hooke's Law, formulated by the 17th-century English scientist Robert Hooke, is the basic law of elasticity. It states that the strain (tendency to deform) of a body is proportional to the stress (deforming force) applied to the body.