Antigen binding proteins that activate GITR are provided. Nucleic acids encoding the antigen binding proteins and vectors and cells containing such nucleic acids are also provided. The antigen binding proteins have value in therapeutic methods in which it is useful to stimulate GITR signaling, thereby inducing or enhancing an immune response in a subject. Accordingly, the antigen binding proteins have utility in a variety of immunotherapy treatments, including treatment of various cancers and infections.
