This proposal focuses on mathematical, computational, and mechanical foundations for designing complex 3D structures that can be built from shape-shifting 2D materials. New kinds of dynamic, shape-shifting matter such as programmable metamaterials, self-folding robotics, and active hydrogels driven by changes in heat, light, or humidity open up an abundance of new possibilities for applications. But with each new material comes new questions about geometry: which shapes can we make, and how? My work aims to dramatically increase the geometric complexity of flexible, shape-shifting objects, by developing new computational tools for shape-shifting design. This work builds on the emerging field of discrete differential geometry, which provides faithful computational analogues for fundamental objects from geometry and physics. As with conventional 3D printing, the goal is to enable anyone to translate intricate designs into physical, deformable mechanisms at the click of a button.