Developments leading to the new practical salinity scale and equation of state for seawater, introduced by the Joint Panel on Oceanographic Tables and Standards (JPOTS), are reviewed. The laboratory measurement used to construct the new empirical formulas for converting conductivity ratios to salinity and for estimating seawater density from salinity, temperature, and pressure were made on samples of standard seawater to minimize the effects of compositional variations. Measured densities were fitted with a standard deviation of 0.0036 kg/m3 at atmospheric pressure and 0.009 kg/m3 over the oceanic pressure range. Natural seawater densities can differ from computer density by as much as 0.05 kg/m3 because of variations in the composition of dissolved salts that are not reflected equivalently in measured conductivity ratios. Differences from the previous Knudsen-Ekman equation of state are also of comparable magnitude. Values of specific volume anomaly for geopotential anomaly computations for estimation of geostrophic currents and transport are not significantly modified. Algorithms adopted by the JPOTS for computing adiabatic lapse rate and potential temperature are compared with formulas derived from the new equation of state. Potential temperatures agree within 2¿10-3 ¿C over the oceanic range of temperature and pressure at salinity of 35.