The present invention relates to amino acid sequences that are capable of binding to serum albumin which, which sequences do not significantly reduce or inhibit the binding of serum albumin to FcRn or significantly reduce the half-life of serum albumin. It further relates to to proteins and polypeptides comprising or essentially consisting of such amino acid sequences； to nucleic acids that encode such amino acid sequences, proteins or polypeptides； to compositions, and in particular pharmaceutical compositions, that comprise such amino acid sequences, proteins and polypeptides； and to uses of such amino acid sequences, proteins and polypeptides.
