Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Distribution of live (green) and dead (red) cells in a microbial biofilm simulated with a three-dimensional cellular automata model. The yellow background is the substratum. This section shows the predicted pattern of viability in an antimicrobial-treated biofilm, in the layer of cells immediately adjacent to the attachment surface. Among the features captured in this model that are noted in real biofilms are hollow cell clusters, antimicrobial tolerance of biofilm in comparison with the susceptibility of free-floating cells, and nonuniform, stochastic patterns of survival. (See related article on page 2005.)