Optimal performance and longevity of high-temperature Concentrated Solar Power (CSP) systems hinge on the stringent thermophysical properties of heat transfer fluids (HTFs). An ideal HTF must possess high thermal conductivity for efficient heat transfer, optimal viscosity to minimize pumping power, and high specific heat capacity for maximizing thermal energy storage. At elevated temperatures, thermal stability is paramount to prevent molecular decomposition, oxidation, and degradation, which can compromise fluid properties and system integrity. Critical parameters for HTFs include thermal conductivity (typically 0.1–1.0 W/m·K), dynamic viscosity balancing flow and heat transfer, and specific heat capacities directly influencing storage capacity. Comprehensive characterization of temperature-dependent properties such as heat capacity, melting point, heat of fusion, vapor pressure, density, and thermal conductivity is essential for accurate engineering calculations in solar receivers and heat exchangers. Ensuring a sufficiently low freezing point is also vital to prevent solidification and mechanical damage, highlighting the continuous need for innovation in HTF and material development for CSP.