Cover photograph (Copyright © 2002, American Society for Microbiology. All Rights Reserved.): Pathogenic bacteria can be tethered to their host cell via adhesion pili, particularly during the initial stages of infection. While they are built from homologous subunits, specific differences between P pili and Hib pili may facilitate survival of bacteria in their respective environmental niches, the urinary tract and the nasopharynx. Three-dimensional reconstructions (left and right) computed from electron microscope images and cartoon drawings (center) highlight structural differences between P pili from Escherichia coli (left and top center) and Hib pili from Haemophilus influenzae (right and bottom center) (See related article on page 4868.)