In biology, phenetics, also known as numerical taxonomy, is an attempt to classify organisms based on overall similarity, usually in morphology or other observable traits, regardless of their phylogeny or evolutionary relation.

Phenetics has largely been superseded by cladistics. However, some biologists continue to use certain phenetic methods, such as neighbor-joining, as a reasonable approximation of phylogeny when cladistic methods are too computationally expensive.

Phenetics must not be confused with phonetics, the study of speech sounds, despite the similarity in pronunciation.