Our knowledge of RNA structure and function has progressed at an astonishingly fast pace in the last five years. Since then, we have seen the X-ray structure of a full ribozyme, the awesome structure of a large domain of a group I intron, and recently the striking structure of the loop E of 5S rRNA. NMR studies have yielded structures, not only of small recurrent loops, but also of several RNA aptamers and of a fragment of the 16S rRNA complexed with an antibiotic. Both methods have also contributed enormously to our understanding of RNA–protein interactions; the richness of the tRNA synthetase interactions is now recognized, whereas the structures of complexes from the spliceosome and the ribosome point to new horizons. The 22 chapters of this new book compose a tribute to the fascinating and ubiquitous versatility of the RNA molecule.