The migration of eukaryotic cells requires a high coordination of molecular activities in space and time. When migrating, cells present a highly polarized state as revealed by the many subcellular biochemical gradients, the directed transport of materials, or the spatially arranged cytoskeletal structures. A complex signaling circuitry orchestrate this coordination, and we are currently trying to understand the logic of this circuitry from biophysical principles. As a main theme, we use light-gated dimerization (non-neuronal optogenetics) to manipulate in space and time the biochemical activities of the RhoGTPases, which are small molecular switches at the core of the signaling network controlling cell polarity and migration. I will present the principle of these acute perturbations and illustrate their application in two selected examples: the understanding of back-to-front coordination in cell polarity and the role of gradient shape in migration.