Thermoelectric phenomenon fundamentally involves the ability to convert thermal energy from a temperature gradient into electrical energy and vice versa by utilizing the benefits of Seebeck effect and Peltier effect. These effects have been introduced in the previous chapter. The performance of thermoelectric materials can be maximized by tailoring the thermoelectric parameters, by requiring high electrical conductivities, large value of Seebeck coefficient, and low thermal conductivities. These thermoelectric parameters are interrelated with each other. Therefore, the key element is to have a thorough knowledge of their dependency as well as their interrelationships for optimizing the Figure of Merit – ZT. This in turn improves the thermoelectric performance resulting, thereby, in increased efficiency of a thermoelectric generator. We consider each of the thermoelectric parameters in this chapter.