For many years two techniques have dominated structural biology – X-ray crystallography and NMR spectroscopy. Traditional cryo-electron microscopy of biological macromolecules produced macromolecular reconstructions at resolution limited to 6–10 Ă…. Recent development of transmission electron microscopes, in particular the development of direct electron detectors, and continuous improvements in the available software, have led to the “resolution revolution” in cryo-EM. It is now possible to routinely obtain near-atomic-resolution 3D maps of intact biological macromolecules as small as ~100 kDa. Thus, cryo-EM is now becoming the method of choice for structural analysis of many complex assemblies that are unsuitable for structure determination by other methods.