Ocean warming contributes to global mean sea level rise by reducing the density of seawater, thus increasing its volume. Freshening of seawater also reduces its density, and this effect contributes to regional sea level variations. However, the effect on global mean sea level rise of ocean freshening by land-ice melt is overwhelmed by the effect of the addition of that melted ice to the ocean. After a brief introduction on the importance of the ocean in the current planetary energy imbalance and the consequences for sea level rise, this article reviews the changing mix of ocean measurements of temperature and salinity, and evolving sampling patterns since the 1950s. Estimates of global sea level rise due to warming and the effects of temperature and salinity on regional sea level change patterns are discussed. The article concludes with an examination of the prospects for accomplishing more global temperature and salinity observations by extending autonomous measurements into the currently poorly sampled ice-covered ocean and the half of the ocean volume below the current 2,000-dbar pressure limit of the Argo array of profiling floats.