Tunneling, or quantum tunneling, takes place when a particle travels through a region that would be forbidden according to the laws of classical physics. Tunneling occurs because quantum wavefunctions extend slightly past the boundaries that define where a particle is allowed to be. For example, in classical physics, an electron is allowed to move through a conductor but not through an insulator. However, if a thin layer of insulator is placed between two conductors, the electron can tunnel through from one conductor to the other because its wavefunction extends into the insulating layer.