This chapter reviews the principal constraints that limit the applicability of phase change materials (PCMs) in latent heat thermal storage (LHTS) systems. Chemical instability, thermodynamic weaknesses, and poor heat transfer behavior are the main issues. When salts are hydrous, incongruent melting can result in phase separation, leading to lower storage potential. In addition, subcooling can retard freezing, which has the deleterious effect of decreasing heat recovery. Also, most PCMs have low thermal conductivity, which limits the rate at which they can charge and discharge. Some measures to enhance the heat transfer are presented in this chapter, including the use of fins, metallic foam, and nanoparticles. Leakage and degradation can be reduced by using encapsulation and composite matrices. It also investigates dynamic PCM systems as a promising economical solution to enhance performance, without resorting to high-expensive materials. In general, while initial costs may be increased, thermal reliability and system efficiency, as well as the cost of implementing PCM-based heat storage systems in the long term, are considerably improved.