Many essential cellular functions require large scale organization of the cell cortex. These include cytokinesis, asymmetric cell division, cell migration, and formation of an epithelium. Extensive organization of the cytoskeleton and cell-cell junctions are required during development to drive changes in the shape of cells, embryos, and tissues. Each of these processes requires establishment and maintenance of metastable domains that serve important cellular functions. The mechanisms by which these domains assemble remain incompletely understood, in part due to the difficulty inherent in functionally dissecting dynamic protein assemblies with current tools. Recently developed optogenetic tools permit light-mediated control of protein activity in live cells at high spatial and temporal resolution. This novel approach provides a powerful means to dissect the underlying molecular mechanism underlying such processes. We will combine the ability to alter the activity of specific molecules with high spatial and temporal resolution with conventional cell biology, imaging, genetic, and biochemical approaches, in order to better understand how cells divide, polarize and shape tissues.