Herpes simplex virus (HSV) entry into cells requires binding of the envelope glycoprotein D (gD) to one of several cell surface receptors. The 50 C‐terminal residues of the gD ectodomain are essential for virus entry, but not for receptor binding. We have determined the structure of an unliganded gD molecule that includes these C‐terminal residues. The structure reveals that the C‐terminus is anchored near the N‐terminal region and masks receptor‐binding sites. Locking the C‐terminus in the position observed in the crystals by an intramolecular disulfide bond abolished receptor binding and virus entry, demonstrating that this region of gD moves upon receptor binding. Similarly, a point mutant that would destabilize the C‐terminus structure was nonfunctional for entry, despite increased affinity for receptors. We propose that a controlled displacement of the gD C‐terminus upon receptor binding is an essential feature of HSV entry, ensuring the timely activation of membrane fusion.