Molten salts are being employed throughout the world as heat transfer fluids and phase change materials for concentrated solar power (CSP) production and storage. In order to design large production facilities, accurate physical and thermodynamic properties of molten salts must be known. Required data include a) melting point; b) viscosity; c) apparent heat of fusion; d) thermal conductivity; e) heat capacity; f) density; g) volumetric expansion; and h) vapor pressure. Data are available for many pure components which make up molten salt mixtures. However, there are some missing or inconsistent numbers in the literature, especially for materials at elevated temperatures. This paper summarizes our most current thermodynamic measurements for some pure salts and mixtures which are of interest as heat transfer fluids and phase change materials (PCM). Specifically, data on the apparent heat of fusion (ΔHfus) and heat capacity (Cp) for a family of nitrate and nitrite salts are reported. These data are critical for estimating costs associated with parabolic trough systems, central receiver towers, and thermal storage tanks.