Solar flux is inherently of very high thermodynamic quality (low entropy). However, the terrestrial use of solar heat at high temperature can be achieved only by means of solar concentrators of the reflecting or refracting type. It is the purpose of this paper to describe the three major design variables of concentrators optical efficiency, heat loss coefficient and heat removal factor. The optical efficiency no embodies many important concentrator properties including mirror surface reflectance and slope, tracking accuracy, receiver transmittance and adsorptance and solar beam incidence angle effects. The heat loss coefficient Uc of a solar concentrator represents its thermal performance and depends upon the relative magnitudes of convection and conduction flux rates, surface emittances of receiver components and operating temperature relative to the environment. The third design parameter-the heat removal factor FR-is a measure of the efficiency of the receiver when viewed as a heat exchanger. Its value is governed by working fluid properties and flow rates as well as by the thermal properties of the receiver material. The principal factors which determine the value of no, Uc and FR are described in the paper.