Quaternary (disambiguation)

The Quaternary is a geologic period.

Quaternary (an adjective meaning "fourth in order" or "composed of four items") may also refer to:
 * Quaternary (chemistry) (see also Quaternary compound and Quaternary phase)
 * Quaternary structure of proteins
 * Quaternary sector of the economy, which encompasses knowledge-based services
 * Quaternary care, health care that includes highly specialized or experimental treatments
 * Quaternary numeral system (base-4) in mathematics
 * Quaternary counting system, as used in some human languages
 * Quaternary (EP), an album by Mötley Crüe
 * Quaternary star system, a star system that contains four stars