Nature manufactures a wide assortment of compounds highly diverse in structure and function. Many of these compounds are therapeutically valuable, and play important roles in maintaining and enhancing human health. A large percentage of these compounds are produced as secondary metabolites by their native hosts. ere are over 20,000 biologically active secondary microbial metabolites, and over 16,000 have antibiotic activity.1 e famous Streptomyces genus alone produces approximately 8,000 known bioactive small molecules. Considering all natural products (1,000,000+), over a quarter of a million display some bioactivity, with 30,000 known to possess antibiotic activity.1 Table 23.1 is a partial list of natural drugs on the market today along with their respective natural hosts and therapeutic value. More natural products (or those derived from natural precursors) are still completing clinical trials, and an excellent review on therapeutics derived from natural products has been published by Mark Butler.2