Selenium is a mineral that plays a role in aging, cancer and chronic diseases, with selenoproteins – proteins that incorporate selenium through the use of an amino acid – now identified as having an important role in antioxidant defense mechanisms. Sharon Rozovsky, from the University of Delaware (Delaware, USA), and colleagues employed state-of-the-science analysis techniques to study selenium in redox biology, revealing the molecular basis by which selenoproteins exert their antioxidant effects.