Genistein is an isoflavone found widely in legumes and other plant species. It is common in many microbial fermentations containing soy or other related plant-based extracts. Genistein has been very widely reported as an antibacterial, insect antifeedant and antitumor active. It also has oestrogenic, bond protective, antioxidant, and reverse transcriptase and tyrosine kinase inhibitory activity. More recently, genistein as a major component of soy products has gained acceptance as a nutraceutical. Genistein is an essential dereplication and bioassay standard in microbial natural product discovery.