The invention provides antibodies that specifically bind to OX40 (CD 134), referred to as OX40 antibodies, anti-OX40 or anti-OX40 antibodies. Invention antibodies that specifically bind to OX40 include mammalian (human, primate, etc.), humanized and chimeric anti-OX40 antibodies. Invention antibodies and antibody subsequences (fragments) that specifically bind to OX40 include purified and isolated antibodies, as well as pharmaceutical formulations thereof, are useful in various methods including treatment, screening and detection methods.