Until recently, the default approach to manufacturing something was some sort of subtractive technique. Subtractive manufacturing (done through a mix of machining, forging, and casting) starts with raw materials like steel or wood and "subtracts" pieces until the desired component is shaped. Think of it like creating a marble sculpture. Additive manufacturing (3D printing) takes a different approach. By building objects from the ground up through one ultra-thin layer a time, new manufacturing possibilities are now possible. Capital intensive equipment is no longer necessarily needed, and conventional design constraints have been lifted. From GE changing its approach to aviation manufacturing, to people rapidly prototyping their own ideas in living rooms, 3D printing has emerged as a new form of manufacturing that's here to stay.