Cell-permeable small organic molecules that rapidly perturb the function of their targets are powerful tools to dissect dynamic cellular processes. Our laboratory focuses on the design, discovery and synthesis of such small molecules. We have generated specific inhibitors for selected protein targets for which we have structural information, such as proteins in the kinesin superfamily. We also synthesize large collections of diverse small molecules from which we can select inhibitors of specific cellular events, such as cell division. Identification of the target of these small molecules enables us to link the inhibition of a known or a novel protein to am observed cellular phenotype. Using state-of-the-art microscopy to image rapid perturbations of protein function by small molecules, we are gaining insight into essential cellular processes.