Cover photograph (Copyright © 2002, American Society for Microbiology. All Rights Reserved.): Atomic force microscopy (AFM) image of a Saccharomyces cerevisiae cell recorded in aqueous solution. The cell (center of the image) is trapped in a porous polymer membrane (surrounding flat area) and shows a 1-μm circular bud scar. In recent years, AFM has emerged as a powerful tool for imaging the topography of microbial cell surfaces. In addition, AFM force measurements can be used to probe the cell surface physical properties, including surface hydrophobicity, surface charges, molecular interactions, surface stiffness, and macromolecular elasticity. (See related article on page 5205.)