Nonribosomal peptides (NRPs) are a type of secondary metabolite with a wide range of pharmacological and biological activities including cytostatics, immunosuppressants or anticancer agents, antibiotics, pigments, siderophores, toxins. NRPs, unlike other proteins, are synthesized on huge nonribosomal peptide synthetase (NRPS) enzyme complexes that are not dependent on ribosomal machinery. Bacteria and fungi are the most common NRPs producers. Furthermore, the presence of these peptides has been confirmed in marine microbes. Nowadays, many of these peptides are used in the treatments of inflammatory, cancer, neurodegenerative disorders, and infectious disease for the development of new therapeutic agents. The structure, function, and synthesis of NRPs, as well as producer microorganisms and their several application areas, are covered in this chapter.