The sequence of steps in budding described here results in a very different mechanistic understanding of filovirus budding. Firstly, the proposed two budding modes, one vertical and one horizontal, can be reconciled as representing different snapshots of a single budding mechanism. Secondly, rather than filoviruses adopting a unique horizontal mode of budding not seen in other systems, the budding process can now be placed within the established framework of other cellular budding events. In the new model, budding is initiated by wrapping of one end of the NC with a hemispherical membrane, and completed by scission at a bud-neck with a classic round cross-section. These are the membrane shapes present during budding and scission events of cellular vesicles and spherical viruses. Thirdly, comparison of our data with published electron micrographs of filamentous virus budding structures suggests that other viruses may also follow the sequence of steps described here, and that rather than being unique, filovirus budding belongs within a more general budding mechanism also adopted by other rod-shaped viruses. For example, budding VSV, a rhabdovirus, can be found protruding perpendicular to cell membranes in infected cells, but the NC can also be seen underneath the cell membrane, with which it associates laterally along one side [35] . The rounded end of the virus, easily distinguished in VSV, seems to associate more tightly with the membrane [43] , and buds first. After budding, under certain preparation conditions, the rear of the virus is seen to show small membrane blebs or instabilities [41] similar in appearance to those described here for MARV. These striking observations are consistent with VSV following the same sequence of budding steps as MARV. A general assembly and budding mechanism for filoviruses and rhabdoviruses might represent a target for future antiviral drugs.