The heme is a ubiquitous iron containing molecule found at the core of many proteins (hemeproteins). The most well-known is hemoglobin involved in transport of oxygen from lung to the cell in many species including humans, and this is one of the many functions of the heme. The cytochrome oxidase present in almost all living organisms consists of two hemes and converts oxygen to water at the final stage of respiration. On the other hand, a heme in cytochrome P450, uses oxygen molecules to carry out drug metabolism, steroid biosynthesis and degradation of toxic substances. Apart from these diverse functions of the heme in different hemeproteins, it also catalyses degradation of toxic peroxides and superoxides. The talk would highlight our efforts in unraveling the molecular origin of the diversity of the functions of the heme and in the development of biocatalysts using modified hemeproteins.