Chemists have long been fascinated by metal loenzymes and their chemistry. The reactivity and selectivity of enzyme processes would be powerful pract ical advances if harnessed in designed transition-metal catalysts. But designing enzyme- like catalysts f rom scratch has proven exceedingly chal lenging. Subst rate select ivi ty in polyfunctional environments and highly reactive intermediates incompatible with the bulk aqueous media are proper ties that are typically too complex and challenging to repl icate in simpl ified, designed systems. Our own ef forts have focused on combining the attributes of enzymes and traditional catalysis, bringing the benefits of polypept ide ligands to bear on completely non-biological transi tion-metal center. Rhodium( I I ) metal lopept ides are proven to be an especially fruitful class of compounds for developing new types of reactivi ty and molecular function. Our ef forts have centered on two main interests: (1) understanding how nature’s ligand of choice—polypeptides—can be used to control the chemistry of non-biological metal center s , and (2) mimicking characteristics of metal loenzymes in designed, non-biological catalysts. Recent achievements include applications of these concepts to small-molecule methodology, protein modi ficat ion based on proximity - driven reactivity, and medicinal organometallic chemistry.