To move forward, migrating cells pull rearward against extracellular matrix and exert traction forces. To elucidate the mechanism of traction force generation in keratocytes, the authors have measured the forces generated against ECM contacts on both the ventral and the dorsal surfaces of the lamella. They used a micromachined substrate to measure forces on the ventral surface and an optical gradient trap to measure forces on the dorsal surface. Both methods determined comparable forces per unit area that were rearward in the front of the lamella, increasing toward the perinuclear region, and eventually changing direction. The rearward traction forces generated throughout the lamella suggest that myosin condensation at the cell body boundary pulls the lamella actin network rearward and pushes the cell body forward.