This chapter recalls the general principles and main formulations useful in the study of thermoelectric coolers. Starting from the general heat diffusion equation, analytical expressions are introduced for the determination of cooling capacity and rate of heat rejection in steady-state conditions. When dealing with the whole refrigeration system, the limits of the steady-state analysis of the individual thermoelectric elements are pointed out, indicating the need for transient analysis supported by experimental evaluations. Then, the energy indicators are illustrated by considering the electrical power consumption, the thermal performance described by the dimensionless figure of merit, as well as the coefficient of performance. Furthermore, the main methods to enhance the thermoelectric cooler performance in refrigeration units are highlighted, with reference to highperformance materials, design aspects and temperature control systems. Finally, indications are reported on some applications of various thermoelectric refrigeration solutions, considering the technical aspects of the performance of these systems.