The present invention provides antibodies that bind to CD3 and methods of using the same. According to certain embodiments, the antibodies of the invention bind human CD3 with high affinity and induce human T cell proliferation. The invention includes antibodies that bind CD3 and induce T cell-mediated killing of tumor cells. In a particular embodiment, there is provided an isolated human antibody or antigen-binding fragment thereof that binds human CD3 with a binding dissociation equilibrium constant (KD) of less than 2 nM as measured in a surface plasmon resonance assay at 25ºC in an antigen-capture format, wherein the antibody or antigen-binding fragment comprises a heavy chain variable region (HCVR) comprising complementarity determining regions HCDR1-HCDR2-HCDR3, and a light chain variable region (LCVR) comprising complementarity determining regions LCDR1-LCDR2-LCDR3, wherein complementarity determining regions have defined sequences.
