This paper reviews and evaluates the experimental works of the static dielectric constant (permittivity) of water and steam over the century. The critically evaluated experimental data are represented by a function of temperature and density. This representation was carefully examined in the light of the criteria for smoothness and physical plausibility. As a result of this work, which was largely stimulated by the activities of the International Association for the Properties of Steam, a new International formulation for the static dielectric constant of water and steam was adopted. This formulation covers a temperature range from 0 to 550 °C and a pressure range up to 500 MPa.