The chapter discusses the meaning and origin of some important classes of secondary metabolites such as alkaloids, terpenoids, tannins, flavonoids, saponins, glycosides, and phenolic compounds, etc., produced by some bacteria, fungi, or plants. Very important drugs that are used clinically are derived from these secondary metabolites. Several reports obtained in scientific journals and books written by different scientists working or who have worked in the fields of natural products medicine were reviewed. These different classes of secondary metabolites have shown activity against varied diseases, and compounds that are of novel structure and activity have been isolated and characterized from them. The chapter highlights the economic impacts of these chemical compounds including their role in improving human and animal health and well-being by serving as sources of some antibiotics, anticancer, anti-inflammatory, antifertility, antidiabetics, analgesics, growth promoters, etc. Secondary metabolites are also used to enhance agricultural productivity, they find uses as pesticides, insecticides, and preservatives. Some folkloric uses of secondary metabolites chemical compounds based on reliable sources of information and genuine scientific investigations are highlighted.