In this review I have tried to describe the progress that has been made in studies of viral envelopes in the last few years. In every particular of structure, biogenesis, and assembly, increased knowledge has increased the apparent similarity between viral envelopes and plasma membranes. Thus, the viral envelopes provide unique experimental opportunities for investigating membranes. We can expect that progress in our understanding of membrane structure will continue through the study of viral envelopes over the next few years--most notably through study of the lateral organization of viral envelopes, and of the synthesis, processing, and mode of action of envelope proteins.