In August 1984 Chuck Hull filed the patent for stereolithography: a process that builds three-dimensional objects layer by layer by hardening photosensitive resin with an ultraviolet beam. The first commercial printer, the SLA-1, reached the market in 1987. The conceptual shift relative to all prior printing history is radical: instead of fixing information onto a surface, the machine manufactures objects. 3D printing opens distributed digital manufacturing — the possibility of producing physical parts from a file, without an assembly line — with implications ranging from industrial prototyping to regenerative medicine.