The trimeric envelope glycoprotein of HIV-1, composed of gp120 and gp41 subunits, remains a major target for vaccine development. The structures of the core regions of monomeric gp120 and gp41 have been determined previously by X-ray crystallography. New insights into the structure of trimeric HIV-1 envelope glycoproteins are now coming from cryo-electron tomographic studies of the gp120/gp41 trimer as displayed on intact viruses and from cryo-electron microscopic studies of purified, soluble versions of the ectodomain of the trimer. Here, we review recent developments in these fields as they relate to our understanding of the structure and function of HIV-1 envelope glycoproteins.