A cut or tear in a material is typically a sign of weakness. Now researchers have created complex 3-D micro- and nanostructures out of silicon and other materials using an assembly method that uses cuts to advantage. The technique can create closed-form 3-D shapes from 2-D material in an instant, like a pop-up children’s book. The work borrows ideas from Kirigami, the ancient Japanese technique for forming paper structures by folding and cutting.