The present invention provides antibodies that bind to the class III variant of EGFR (EGFRvIII) and methods of using the same. According to certain embodiments, the antibodies of the invention bind human EGFRvIII with high affinity. The antibodies of the invention may be fully human antibodies. The invention includes anti-EGFRvIII antibodies conjugated to a cytotoxic agent, radionuclide, or other moiety detrimental to cell growth or proliferation. The antibodies of the invention are useful for the treatment of various cancers.