The structure of proteins determines their function. The front cover shows a ribbon diagram of fragments of the protein cystic fibrosis transmembrane regulator; the back cover shows the drug molecule saquinavir bound into the active site of HIV-1 protease. This issue of the IBM Systems Journal contains papers describing the information-intensive computational methods that provide a basic understanding of life at the molecular level. The molecular diagrams on the covers were generated by F. Suits, using software developed at IBM, from data in the Protein Data Bank (see pages 254 and 255).