Abstract
Secondary metabolites are low molecular mass products of secondary metabolism which are usually produced by microorganisms experiencing stringent conditions. These metabolites are not essential for growth but serve diverse survival functions in nature. Besides offering survival advance to the producing organisms, they have several medicinal uses such as antibiotics, chemotherapeutic drugs, immune suppressants, and other medicines which benefited human society immensely for more than a century. This chapter provides an overview of various functions these secondary metabolites offer in nature from single-cell organisms to multicellular organisms. Furthermore, this chapter also discusses the underlying mechanisms behind their diverse functions and how these are regulated and synthesized under non-viable environmental conditions.