Electron cryomicroscopy (cryoEM) of biological specimens preserved by vitrification in water ice has made great strides in the last decade. The atomic structure of most biological macromolecules can, at least in principle, be determined by direct imaging using bright field phase contrast. Major technological advances – in electron imaging hardware, data analysis software, and cryogenic specimen preparation technology – continue at pace and contribute to the exponential growth in the number of atomic structures determined by cryoEM. It is now likely, that within a few years we will have structures for hundreds of thousands of unique protein and nucleic acid molecular complexes. But the answers to many important questions in biology would become obvious if we could identify these structures precisely inside cells with quantifiable error. In the context of an abundance of known structures, it is appropriate to now consider the current state of electron cryomicroscopy for frozen specimens prepared directly from cells, and try to understand what technology can be brought to bear on this goal, both now and in the foreseeable future.
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