The present invention provides isolated anti-human NKG2D monoclonal antibodies useful for therapeutic applications in humans. Typically, the antibodies are fully human or humanized to minimize the risk for immune responses against the antibodies when administered to a patient. Preferred antibodies include human monoclonal antibodies MS and 21F2. As described herein, other antigen-binding molecules such as, e.g., antigen-binding antibody fragments, antibody derivatives, and multi-specific molecules, can be designed or derived from such antibodies.