Cosmetics are products intended for application to the skin and hair with the purpose of cleansing, beautifying, enhancing attractiveness, or improving appearance. Among the active ingredients commonly used in such preparations, there is a growing worldwide trend toward incorporating plant-derived substances and ingredients obtained from agroindustrial residues, owing to their commercial appeal, sustainability, perceived safety, and rich phytochemical composition, often associated with synergistic and multifunctional effects. These botanical extracts and upcycled byproducts are particularly rich in secondary metabolites, which display high structural diversity and broad biological activity. Among these, phenolic compounds are associated with a wide range of desirable cosmetic properties, such as photoprotective, antiaging, moisturizing, antioxidant, astringent, antiirritant, and antimicrobial activities. In this chapter, we present and discuss the most promising phenolic compounds for use in cosmetic formulations, highlighting how phenolic-rich ingredients can contribute to the development of safer, more effective, and more sustainable cosmetic products.