The piezoelectric effect is the ability of certain materials to generate an electric charge in response to applied mechanical stress. This effect is reversible, meaning that materials exhibiting the direct piezoelectric effect (the generation of electricity when stress is applied) also exhibit the converse piezoelectric effect (the generation of stress when an electric field is applied) . The piezoelectric effect results from the linear electromechanical interaction between the mechanical and electrical states in crystalline materials with no inversion symmetry. Piezoelectric materials include crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins.

The piezoelectric effect is used in many applications, such as the production and detection of sound, generation of high voltages, electronic frequency generation, microbalances, and ultra-fine focusing of optical assemblies. It is also the basis of a number of scientific instrumental techniques with atomic resolution, such as scanning probe microscopes. The piezoelectric effect also has its use in more mundane applications, such as acting as the ignition source for cigarette lighters.

The direct piezoelectric effect was first seen in 1880 by Pierre and Jacques Curie. The inverse piezoelectric effect occurs in the opposite way when atoms are subjected to electrical pressure when a voltage is put across a piezoelectric crystal. The atoms will then have to move to rebalance themselves, and this is what causes piezoelectric crystals to deform when voltage is applied across them.

In summary, the piezoelectric effect is the ability of certain materials to generate an electric charge in response to applied mechanical stress. This effect is reversible, and it is used in many applications, such as the production and detection of sound, generation of high voltages, and microbalances.