Complementarity may refer to:

• Complementarity (molecular biology), a property of nucleic acid molecules in molecular biology
• Complementarity (physics), the principle that objects have complementary properties which cannot all be observed or measured simultaneously
• Complementarity theory, a type of mathematical optimization problem
• Quark–lepton complementarity, a possible fundamental symmetry between quarks and leptons

• Complementarianism, a theological view that men and women have different but complementary roles
• Complementary good, a good for which demand is increased when the price of another good is decreased
• An element of interpersonal compatibility in social psychology
• The principle that the International Criminal Court is a court of last resort

• Complementarity-determining region, part of the variable chains in immunoglobulins
• Complementary angles, in geometry
• Self-complementary graph, in graph theory
• Yin and yang, complementary relation between apparent opposites in Chinese philosophy
• Complimentary (disambiguation)
• Complement (disambiguation)