The genus Senna is a member of the legume family (Fabaceae) and has about 300 species that are widespread in tropical and subtropical regions of Africa, Asia, Europe, and Latin America. In folk medicine, certain species of Senna are known for their antimicrobial, anti-inflammatory, and antipyretic properties and for their use against microbial infections and malaria. Senna species are sources of valuable secondary metabolites including alkaloids, anthraquinones, flavonoids, tannins, glycosides, steroids, terpenoids, saponins, and essential oils. Numerous biological studies have demonstrated that both extracts and isolated pure compounds of the genus Senna have a broad range of in vitro and in vivo pharmacological applications, including antidiabetic, antimicrobial, anti-oxidative, anti-fever, antinociceptive, antidepressant, anti-inflammatory, and anticancer activities. The aim of this chapter is to describe the phytochemicals of selected secondary metabolites contained in the genus Senna and to critically select extracts and pure compounds and their biological properties, such as anticancer, cytotoxic, anti-inflammatory, and antimicrobial activity, providing a useful literature to confirm their wide application in medicine.