We describe the basal sauropodomorph Eoraptor lunensis, based on the nearly complete holotypic skeleton and referred specimens, all of which were discovered in the Cancha de Bochas Member of the Ischigualasto Formation in northwestern Argentina. The lightly built skull has a slightly enlarged external naris and a spacious antorbital fossa with a prominent, everted dorsal margin and internal wall lacking any pneumatic extensions into surrounding bones. The tall quadrate is lapped along its anterior margin by the long, slender ventral process of the squamosal, and the lower jaw has a mid-mandibular joint between a tongue-shaped splenial process and a trough in the angular. All but the posterior-most maxillary and dentary crowns have a basal constriction, and the marginal denticles are larger and oriented more vertically than in typical theropod serrations. Rows of rudimentary palatal teeth are present on the pterygoid. Vertebral centra are hollow, although not demonstrably pneumatized, and all long bones have hollow shafts. The radius and ulna are more robust, the manus proportionately shorter, and the manual unguals less recurved than in the contemporaneous basal theropod Eodromaeus murphi. An outstanding feature of the manus of Eoraptor is the twisted shaft of the first phalanx of the pollex, which deflects medially the tip of the ungual as in basal sauropodomorphs. The long bones of the hind limb have more robust shafts than those of Eodromaeus, although in both genera the tibia remains slightly longer than the femur.