This invention relates to soluble forms of G glycoprotein from Hendra and Nipah virus. In particular, this invention relates to compositions comprising soluble forms of G glycoprotein from Hendra and Nipah virus and also to diagnostic and therapeutic methods using the soluble forms of G glycoprotein from Hendra and Nipah virus. Further, the invention relates to therapeutic antibodies including neutralizing antibodies, and vaccines for the prevention and treatment of infection by Hendra and Nipah viruses.