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The matrix protein VP40 is an indispensable component of viral assembly and budding by the Ebola virus. VP40 is a monomer in solution, but can fold into hexameric and octameric states, two oligomeric conformations that play central roles in the Ebola viral life cycle. While the X-ray structures of monomeric and octameric VP40 have been determined, the structure of hexameric VP40 has only been solved by three-dimensional electron microscopy (EM) to a resolution of »30 Å. In this paper, we present the reWnement of the EM reconstruction of truncated hexameric VP40 to »20 Å and the construction of an all-atom model (residues 44–212) using the EM model at »20 Å and the X-ray structure of monomeric VP40 as templates. The hexamer model suggests that the monomer– hexamer transition involves a conformational change in the N-terminal domain that is not evident during octamerization and there-fore, may provide the basis for elucidating the biological function of VP40. Published by Elsevier Inc