Cover photograph (Copyright © 2004, American Society for Microbiology. All Rights Reserved.): Three-dimensional electron microscopy bridges the gap between knowledge of bacterial architecture at optical resolution and knowledge of atomic structures of individual components obtained using X-ray crystallography. The upper images are low-resolution views of whole bacteria obtained using optical and scanning microscopy. The lower images show expanded views of a segmented tomogram obtained from a small region of an Escherichia coli cell engineered to overproduce Tsr. The information in the tomogram is combined with an atomic model of a typical chemotaxis receptor to generate a plausible three-dimensional arrangement of chemotaxis receptors in the cell membrane. (See related article on page 5052.)