Arising from the inabilities of X-ray diffraction and NMR to resolve the structures of very large biological aggregates previously e.g., multimer protein complexes, ribosome Electron microscopy (EM) sometime able to have 3-4 Åto allow us to recognize features such as protein helices and sheets An exciting idea being to combine electron microscopy with separate high-resolution X-ray crystal structures of the component proteins Acquiring a full atomic model of the entire complex