The present invention encompasses PRLR binding proteins. Specifically, the invention relates to antibodies that are chimeric, CDR grafted and humanized antibodies. Preferred antibodies have high affinity for hPRLR and neutralize hPRLR activity in vitro and in vivo. An antibody of the invention can be a full-length antibody or an antigen-binding portion thereof. Methods of making and methods of using the antibodies of the invention are also provided. The antibodies, or antibody portions, of the invention are useful for detecting hPRLR and for inhibiting hPRLR activity, e.g., in a human subject suffering from a disorder in which hPRLR activity is detrimental. Also included in the invention are anti-PRLR antibody drug conjugates (ADCs).