A major question in developmental biology is how tissues and organs acquire their shape through the process of morphogenesis. Basic considerations from mechanics imply that tissues are shaped by dynamical changes in (1) cellular forces and (2) tissue material properties. The predominant approach to morphogenesis has consisted largely of genetics and imaging, neither of which is sufficient to quantitatively determine either the forces or tissue properties. Here we propose to measure material tissue properties directly, using calibrated micro-cantilevers to probe tissue with subcellular resolution, in combination with lightsheet microscopy to quantify deformations. From a comprehensive map of material properties and cellular dynamics, we will be able to computationally infer the pattern of forces driving these dynamics uniquely. Using Drosophila germband extension as a model, we will apply our approach to determine the physical mechanisms underlying cell intercalation, rosette formation and resolution, and tissue elongation. Our methods are in principle applicable to any developmental system.