Origami tessellations are made from a single piece of paper, which is folded in a repeating pattern. Figure l.a shows an example of a crease pattern for an origami tessellation. This pattern was created with the aim of producing a finished pattern of repeating "heart" shapes. The problem of finding tessellations which can be folded is difficult because the paper must not be stretched or cut, and must end up as a flat sheet, so this imposes many conditions on the pattern to be folded. An understanding of the geometry of tessellations and of paper folding is required.