The present application describes antibodies that selectively bind human FcγRIIB, with little or no binding to other human FcγRs, e.g., human FcγRIIA. The invention also provides isolated bispecific antibodies comprising an antibody that selectively binds FcγRIIB, and a second antibody that specifically binds an activating receptor. Various uses, including therapeutic uses, for those antibodies are also described, including administration with anti-tumor antibodies and methods of inhibiting immune responses and suppressing histamine release.