This invention provides constructs comprising a protein scaffold, wherein the scaffold comprises Domain III, Domain IIIa, or Domain IIIb of human serum albumin or a polypeptide having substantial sequence identity to the Domain III, the Domain IIIa, or the Domain IIIb; and a targeting moiety in covalent linkage to the protein scaffold; and a therapeutic moiety and/or an imaging moiety in covalent linkage to the protein scaffold. The scaffold can be modified to tune the serum pharmacokinetics of the construct. In addition to methods of making the constructs, therapeutic, imaging and diagnostic uses of the constructs are also provided.