In this study we use electron tomography (ET) to describe and analyse in 3D the structure of MARV budding intermediates and released viruses at different stages of infection. In contrast to conventional EM of ultrathin sections, ET allows complete MARV virions and budding structures to be studied in 3D. This permits unambiguous determination of virus morphology, dimensions, stage of budding and position relative to the infected cell. The samples are prepared by high-pressure freezing followed by embedding in resin and staining with heavy metals. Unlike cryo-ET of vitreous samples, this method is not appropriate for the study of high-resolution protein structure. Nevertheless, it gives excellent preservation of the features studied here such as membranes and protein assemblies including viral NCs [37, 38] . It also has, for this particular purpose, substantial advantages over cryo-ET. The features of interest are imaged at much higher contrast, including at high tilt angles. The samples are also easier to handle and stable under the electron beam, allowing efficient screening, which facilitates the collection of larger datasets.