Cell adhesion to the extracellular matrix (ECM) is necessary for fundamental cellular processes such as survival, migration, and differentiation. Adhesion is mediated by integrin receptors, which recruit multiprotein adhesion complexes to sites of attachment to the ECM. Adhesion complexes provide a structural connection between the ECM and cytoskeleton, transmit mechanical force, and act as signaling hubs to control cell behavior. Recent high-resolution imaging studies of adhesion sites reveal some aspects of their spatial organization and provide insights into their function at the molecular level. © 2011 American Association for the Advancement of Science. All Rights Reserved.