Put simply, a 3D printer is a device which prints real three-dimensional objects rather than flat images onto two-dimensional sheets of paper. The designs for the 3D objects are stored in modelling software on a computer and can be created from scratch or input via a 3D scanner. Various technologies exist, but all currently construct models by building them from layers of material, one on top of the other, which are fused together during the process. Working machines and even electrical circuits can be printed in this way.