Complementary distribution in linguistics refers to the relationship between two elements where one element can be found only in a particular environment and the other element can be found only in the opposite environment. It often indicates that two superficially different elements are in fact the same at a deeper level.

Complementary distribution is commonly applied to phonology, where similar phones in complementary distribution are usually allophones of each other. For instance, in English, and [pʰ] are allophones of the phoneme /p/ because they occur in complementary distribution. [pʰ] always occurs when it is the syllable onset and followed by a stressed vowel (i.e. in the word pin). [p] occurs in all other situations (i.e. in the word spin).

There are cases where elements are in complementary distribution, but are not considered allophones. For example in English [h] and [ŋ] (engma, written as "ng" in English) are in complementary distribution, since [h] only occurs at the beginning of a syllable and [ŋ] only at the end. But because they have so little in common they are still considered separate phonemes.