CP symmetry is preserved when the laws of physics remain unchanged if a particle’s electric charge is inverted (charge conjugation, C) and its spatial coordinates are mirrored (parity, P). In other words, the particle's interactions "look" the same in the “CP mirror”.

CP violation occurs when this symmetry is broken. Particle interactions can be described as CP-even (symmetric under CP transformations), CP-odd (asymmetric under CP transformations), or a mixture of both (described by the CP mixing angle and implying CP violation).