This page is about the scientific concept of relativity, for philosophical or sociological theories about relativity see Relativism. The theory of relativity, or simply relativity, generally refers specifically to two theories of Albert Einstein: special relativity and general relativity. However, the word "relativity" is sometimes used in reference to Galilean invariance.

The term "theory of relativity" was coined by Max Planck in 1908 to emphasize how special relativity (and later, general relativity) uses the principle of relativity.