Provided herein are binding proteins comprising one or more immunoglobulin Fc region hinge, CH2, and / or CH3 domain wherein one or more hinge and / or constant region CH2 and / or CH3 domain is modified to alter the binding protein's binding affinity and / or specificity for a cognate receptor (e.g., an Fc receptor) and / or to impart one or more new binding specificity(ies) to the hinge and / or constant region that the corresponding unmodified immunoglobulin does not possess (e.g., affinity for distinct class of cognate receptor distinct from the class of cognate receptor to which the unmodified binding protein specifically binds). Binding proteins according to the present invention include, for example, modified antibodies, antibody fragments, recombinant binding proteins, and molecularly engineered binding domain-immunoglobulin fusion proteins, including small modular immunopharmaceutical products (SMIP™ products).