Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Retention of Cryptosporidium parvum oocysts (red) in a Pseudomonas aeruginosa biofilm (green), resolved by confocal microscopy. Interaction with biofilms can strongly influence environmental transmission of water-borne pathogens such as C. parvum. As shown in the related article, biofilm morphology strongly influences oocyst capture. Image obtained by Kristin Searcy. (See related article on page 6242.)