Book excerpt: Behind the neologism “ribozymes” lies a family of fascinating molecules, ribo-enzymes, which have been relatively little studied. These catalytically active RNAs are found in all strata of life, from viruses to the human genome. At the end of the 1970s, the discovery of a catalytic RNA nestled in an intron, followed by another involved in the maturation of transfer RNAs, led to the discovery of new ribozymes and the transition from a strictly “proteocentric” vision, inherited from the dogma of molecular biology, to a more “nucleocentric” one. Since then, a variety of ribozymes have been identified in genomes, where their functions often remain mysterious. Looking at Ribozymes traces the discovery of these molecules and presents a picture of their functional diversity, catalytic mechanisms and distribution within the tree of life.