The composition of the extracellular matrix (ECM) surrounding cells is key to their behavior: it modulates their ability to proliferate, differentiate, and migrate (Giancotti and Ruoslahti 1999). ECM components can signal directly to cells through transmembrane receptors such as integrins, and can also present soluble cytokines and growth factors to cells. The morphology of cells varies greatly depending on the composition of the extracellular matrix to which they are exposed, but the molecular basis for these differences has not been clarified. Now, two papers in this issue of The Journal of Cell Biology (Adams and Schwartz 2000; Wenk et al. 2000) show that these variations in cell morphology reflect differential activation of specific Rho GTPases.