The CP operation is a combination of charge conjugation (C) and parity (P). In most interactions, CP is conserved, which means that the interaction proceeds exactly the same way if the CP operation is performed on the interacting particles. If CP is conserved, particles with opposite charge and parity will interact in the same way as the original particles. CP violation occurs when an interaction proceeds differently when the CP operation is performed—particles with opposite charge and parity interact differently than the original particles. CP violation was first observed in neutral kaon systems.