Parity, Charge Conjugation, and Time Reversal in the Gravitational Interaction

Some consequences of possible violation of parity ($P$), charge conjugation ($C$), time reversal ($T$), and $\mathrm{TCP}$ invariance in the gravitation interaction are discussed and compared with existing experimental evidence. The evidence is suggestive of $\mathrm{TCP}$ (or $\mathrm{CP}$ or $C$) invariance, but one cannot rule out separate violation of $P$, $C$, and $T$.