Living things on Earth depend on heme – the iron cyclic tetrapyrrole complex that harnesses iron’s oxidizing powers. Heme is toxic, but Nature has evolved ways to control it. One way is breaking it with heme oxygenase which lowers its levels and begins the formation of linear tetrapyrroles called bilins. Bilins occur in many variations, often colorful, sometimes in abundance, and in animals, plants and microbes. Contrary to early notions, bilins are not only waste products of heme degradation. They are increasingly appreciated for their diverse roles such as sensing and gathering light, regulating growth and aging, responding to inflammatory conditions, and influencing behavior. The diverse functions of bilins are exploited with discoveries and uses of bioactive bilins for salutary benefits in medicine and

agriculture. Opportunities for finding new bioactive bilins and applications will grow as knowledge of bilin biology and

capabilities for producing bilins continue to expand.