Vortigaunts are a semi-humanoid race with one head, two legs, two arms and a smaller third arm growing out of the torso. They have mottled, greenish-brown skin, a large red eye with several smaller eyes around it, breathing tubes on either side of the mouth and two-digit hands. Vortigaunt enslaved by the Nihilanth or Combine have metallic shackles on their arms, a collar around their necks and plates covering the crotch area. Free Vortigaunt have no apparel at all.
Vortigaunt possess a unique ability to generate and manipulate electrical energy. They have been known to project electrical arcs as a form of attack and also have used it to charge machinery. They also possess some kind of astral awareness that they refer to as the "Vortessence". This force is described by them as being "woven into the fabric of the universe itself" and allows the Vortigaunt to communicate telepathically and affords them a greater understanding of the machinations of the cosmos and all life within it.