This chapter describes the design and development of cell-based assays, in which quantitation of the intracellular translocation of a target protein—rather than binding or catalytic activity—provides the primary assay readout. These are inherently high content assays, and they provide feedback on cellular response at the systems level, rather than data on activities of individual, purified molecules. Multiple protein translocation assays can be used to profile cellular signaling pathways and they can play a key role in determination of mechanism of action for novel classes of compounds with therapeutic potential. This assay technology has developed from laboratory curiosity into main stream industrial research over the past decade, and its promise is beginning to be realized as data acquisition and analysis technology evolve to take advantage of the rich window into systems biology provided by translocation assays.