The present invention relates to monoclonal antibodies that bind or neutralize Hendra or Nipah virus. The invention provides such antibodies, fragments of such antibodies retaining Hendra or Nipah virus-binding ability, fully human antibodies retaining Hendra or Nipah virus-binding ability, and pharmaceutical compositions including such antibodies. The invention further provides for isolated nucleic acids encoding the antibodies of the invention and host cells transformed therewith. Additionally, the invention provides for prophylactic, therapeutic, and diagnostic methods employing the antibodies and nucleic acids of the invention.