Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): Biofilms are often associated with a distinctive architecture characterized by mushroom-shaped macrocolonies separated by fluid-filled channels, as illustrated in a top-down view of a 6-day-old Pseudomonas aeruginosa biofilm labeled with red and green fluorescent markers. It appears that maintenance of biofilm architecture, as is the case with the formation of these structures, is also under the active control of this organism. (See related article on page 1027; see also related article on page 699.)