A new 3-D printing method uses simple hardware and sophisticated imaging software inspired by computed tomography (CT) scans to rapidly generate complex objects (Science 2019, DOI: 10.1126/science.aau7114). The method produces objects with very smooth surfaces and could be used to mass customize ergonomic tools and furniture or make optical components. “Most current 3-D printers build up components layer by layer,” says Hayden Taylor, a mechanical engineer at the University of California, Berkeley, whose group developed the new method in partnership with the lab of Christopher Spadaccini of the Lawrence Livermore National Laboratory. The standard approach can be slow, and it produces parts that are rough and mechanically weak. Taylor and Spadaccini wanted to print the entire volume of an object at once. They were inspired by the 3-D imaging used to make CT scans. The medical imaging technique rotates a scanner around a patient’s body and constructs a 3-D image from reflected X-rays. The new printing method does this in reverse. The researchers developed software to turn a 3-D design into a light field that’s projected into a rotating vat of photocurable materials. When the vat completes its rotation after 30 s to 5 min, the object is printed. This can be done using an off-the-shelf movie projector. Because the object is not printed on any kind of support, and does not move relative to the vat, it’s possible to print using even very viscous or fragile materials, such as hydrogels. And this technique, unlike most 3-D printing methods, can be used to “overprint” customized parts around an existing object, such as a personalized handle around a metal screwdriver blade.