The optical properties of bulk and thin‐film Zn3P2have been measured at room temperature over the range 0.5–5.0 eV, with emphasis on the region of the interband absorption edge. The bulk absorption edge is found to be exponential in energy for values of absorption coefficient less than about 1500 cm−1. The thin‐film absorption edge, when freed of spurious absorptance due to scattering, is also found to be exponential over this range although shallower in slope. Analysis of the thin‐film data at higher values of absorption coefficient is inconclusive with respect to the nature of the edge. Nevertheless, indirect evidence suggests that the optical gap is probably direct and lies in the neighborhood of 1.6 eV. Measurements of refractive index in the near‐infrared yieldn=3.3±0.1 in the long‐wavelength limit. The ultraviolet reflectivity spectrum is redetermined, and found to differ substantially from earlier reports. Results are discussed in terms of the Dow‐Redfield model of exponential absorption edges, the effects of spin‐orbit and crystal‐field splittings, and effects arising from the equilibrium distribution of bond lengths peculiar to this material. It is concluded that the optical properties of Zn3P2thin films are suitable for use in photovoltaic cells, provided antireflection coatings are employed.