The present invention provides antibodies that bind to prolactin receptor (PRLR) and methods of using the same. According to certain embodiments, the antibodies of the invention bind human PRLR with high affinity. In certain embodiments, the invention includes antibodies that bind PRLR and block prolactin-mediated cell signaling. In other embodiments, the invention includes antibodies that bind PRLR but do not block prolactin-mediated cell signaling. The antibodies of the invention may be fully human antibodies. The invention includes anti-PRLR antibodies conjugated to a cytotoxic agent, radionuclide, or other moiety detrimental to cell growth or proliferation. The antibodies of the invention are useful for the treatment of various cancers as well as other PRLR-related disorders. The present invention also includes antibody drug conjugates comprising an antibody or antigen-binding fragment thereof that specifically binds a class I cytokine receptor, wherein the antibody or antigen-binding fragment thereof is conjugated to a cytotoxic agent.