Glycoprotein M (gM) is conserved among herpesviruses. Important features are its 6-8 transmembrane domains without a large extracellular domain, localization to the virion envelope, complex formation with another envelope glycoprotein, glycoprotein N (gN), and role in virion assembly and egress. In varicella-zoster virus (VZV), the gM homolog is encoded by ORF50. VZV gM is predicted to be an eight-transmembrane envelope glycoprotein with a complex N-linked oligosaccharide. It mainly localizes to the trans-Golgi network, where final virion envelopment occurs. Studies in which VZV gM or its partner gN were disrupted suggest that the gM/gN complex plays an important role in cell-to-cell spread. Here, we summarize the biological features of VZV gM, including our recent findings on its characterization and function.