Physicists have gotten really good at taking pictures of tiny things. With the help of high-energy x-rays created by synchrotrons and powerful lasers, they’ve imaged everything from chemical nanostructures to proteins to living cells. But they kept hitting a wall when it came to creating 3D images of single biological particles like viruses. Two-dimensional images were easy. All they had to do was record the diffraction patterns that were produced when pulses of ultrabright x-ray light traveled through the particle, and they’d get a snapshot of the molecule or organism. But because they had no idea how the particle was oriented in space when each picture was taken, they had no way of stitching multiple 2D images together to create a 3D picture. Now, researchers working with the Linac Coherent Light Source at SLAC National Accelerator Laboratory in Menlo Park, California, have figured out how to overcome that problem. By tinkering with an algorithm devised in 2009, they figured out how to extract information about a particle’s orientation from just a messy 2D diffraction pattern. Then they used that information to assemble hundreds of such patterns into a coherent 3D image that reveals both the external shape and internal structure of the particle, they reported yesterday in Physical Review Letters. They tested their technique by imaging mimivirus (above), a particularly large virus that is probably not infectious. But they say the technique should be able to handle much smaller and more dangerous viruses, including influenza, herpes, and HIV.