A selection rule in atomic spectra stating that spectral lines associated with electric-dipole radiation must arise from transitions between states of opposite parity. The Laporte selection rule was discovered by Otto Laporte (1903–71) in 1924 and independently by Henry Norris Russell (1877–1957), also in 1924. In the case of magnetic-dipole and quadrupole radiation the selection rule for spectral lines is the opposite of the Laporte rule, i.e. transitions are only allowed between states of the same parity in these cases.

Because parity is invariant under crystal field splittings, where a crystal field has inversion symmetry the Laporte selection rule means that electric dipole transitions are forbidden between energy levels in which the splitting is due to a crystal field. Thus d–d electric dipole transitions are forbidden by the rule where the crystal field has inversion symmetry. This is the case for octahedral crystal fields but not tetrahedral crystal fields. Transitions that are forbidden by the rule can occur weakly for various reasons, such as vibrations of the ions breaking the inversion symmetry of a complex.