The heat capacity of selenium from 0 K to 1000 K is reviewed using measurements on 20 samples reported in the literature. A set of recommended data for trigonal, monoclinic, glassy, and molten selenium is derived. Ring‐chain equilibrium parameters are critically evaluated. Entropy, enthalpy, and Gibbs energy functions are calculated. Selenium is a model compound for a monoatomic, linear macromolecule. This paper is first in a series which will ultimately cover all heat capacity measurements on linear macromolecules.