Reciprocity theorem may refer to:
- Quadratic reciprocity, a theorem about modular arithmetic
- Frobenius reciprocity theorem for group representations
- Stanley's reciprocity theorem for generating functions
- Reciprocity (engineering), theorems relating signals and the resulting responses
- including Reciprocity (electrical networks), a theorem relating voltages and currents in a network
- Reciprocity (electromagnetism), theorems relating sources and the resulting fields in classical electromagnetism
- Tellegen's theorem, a theorem about the transfer function of passive networks
- Reciprocity law for Dedekind sums
- Betti's theorem in linear elasticity