This section examines the ecological and economic considerations of phase change materials (PCMs) in the context of sustainable energy systems. They are an efficient way to reduce a building’s heating and cooling loads, decreasing the costs incurred over time. However, wide use is restrained by expensive production and quick profit return. The environmental impact is estimated by using Life Cycle Assessment (LCA), and it is found that fossil-based PCMs, such as paraffins, have large carbon footprints in production. By comparison, bio-based and inorganic salt hydrate PCMs pose greener alternatives, although cost and scale still present challenges. Sustainability is a balance between environmental efficacy and economic viability. This chapter explores desired approaches, such as the improvement of material durability, the establishment of recycling and recovery techniques, and market maturation concerning eco-efficient PCMs. Overcoming these barriers delineates PCMs as key technologies enabling low-carbon energy systems and global sustainability.