The present invention provides molecules, including proteins, more particularly, immunoglobulins whose in vivo half-lives are altered (increased or decreased) by the presence of an IgG constant domain, or FcRn binding fragment thereof (e.g., an Fc region or hinge-Fc region) (e.g., from a human IgG, e.g., human IgG1), that have modifications of one or more of amino acid residues in at least the CH3 domain.
