An Fc construct comprising: a). a first polypeptide having the formula A-L-B; wherein i). A comprises a first Fc domain monomer; ii). L is a linker; and iii). B comprises a second Fc domain monomer; b). a second polypeptide having the formula A'-L'-B'; wherein i). A' comprises a third Fc domain monomer; ii). L' is a linker; and iii). B' comprises a fourth Fc domain monomer; c). a third polypeptide that comprises a fifth Fc domain monomer; and d). a fourth polypeptide that comprises a sixth Fc domain monomer; wherein said A of said first polypeptide and said A' of said second polypeptide combine to form a first Fc domain, said B of said first polypeptide and said fifth Fc domain monomer combine to form a second Fc domain, and said B' of said second polypeptide and said sixth Fc domain monomer combine to form a third Fc domain; wherein said first Fc domain monomer and said third Fc domain monomer comprise complementary dimerization selectivity modules that promote dimerization between said first Fc domain monomer and said third Fc domain monomer; wherein said second Fc domain monomer and said fifth Fc domain monomer comprise complementary dimerization selectivity modules that promote dimerization between said second Fc domain monomer and said fifth Fc domain monomer; wherein said fourth Fc domain monomer and said sixth Fc domain monomer comprise complementary dimerization selectivity modules that promote dimerization between said fourth Fc domain monomer and said sixth Fc domain monomer; wherein each of said Fc domain monomers is an IgG1 Fc domain monomer; and wherein said complementary dimerization selectivity modules are selected from: dimerization selectivity modules comprising an engineered cavity into the C H 3 domain of one of said Fc domain monomers and an engineered protuberance into the C H 3 domain of the other of said Fc domain monomers, wherein said engineered cavity and said engineered protuberance are positioned to form a protuberance-into-cavity pair of Fc domain monomers; and dimerization selectivity modules comprising a negatively-charged amino acid into the C H 3 domain of one of said domain monomers and a positively-charged amino acid into the C H 3 domain of the other of said Fc domain monomers, wherein said negatively-charged amino acid and said positively-charged amino acid are positioned to promote formation of an Fc domain. a). a first polypeptide having the formula A-L-B; wherein i). A comprises a first Fc domain monomer; ii). L is a linker; and iii). B comprises a second Fc domain monomer; i). A comprises a first Fc domain monomer; ii). L is a linker; and iii). B comprises a second Fc domain monomer; b). a second polypeptide having the formula A'-L'-B'; wherein i). A' comprises a third Fc domain monomer; ii). L' is a linker; and iii). B' comprises a fourth Fc domain monomer; i). A' comprises a third Fc domain monomer; ii). L' is a linker; and iii). B' comprises a fourth Fc domain monomer; c). a third polypeptide that comprises a fifth Fc domain monomer; and d). a fourth polypeptide that comprises a sixth Fc domain monomer; wherein said A of said first polypeptide and said A' of said second polypeptide combine to form a first Fc domain, said B of said first polypeptide and said fifth Fc domain monomer combine to form a second Fc domain, and said B' of said second polypeptide and said sixth Fc domain monomer combine to form a third Fc domain; wherein said first Fc domain monomer and said third Fc domain monomer comprise complementary dimerization selectivity modules that promote dimerization between said first Fc domain monomer and said third Fc domain monomer; wherein said second Fc domain monomer and said fifth Fc domain monomer comprise complementary dimerization selectivity modules that promote dimerization between said second Fc domain monomer and said fifth Fc domain monomer; wherein said fourth Fc domain monomer and said sixth Fc domain monomer comprise complementary dimerization selectivity modules that promote dimerization between said fourth Fc domain monomer and said sixth Fc domain monomer; wherein each of said Fc domain monomers is an IgG1 Fc domain monomer; and wherein said complementary dimerization selectivity modules are selected from: dimerization selectivity modules comprising an engineered cavity into the C H 3 domain of one of said Fc domain monomers and an engineered protuberance into the C H 3 domain of the other of said Fc domain monomers, wherein said engineered cavity and said engineered protuberance are positioned to form a protuberance-into-cavity pair of Fc domain monomers; and dimerization selectivity modules comprising a negatively-charged amino acid into the C H 3 domain of one of said domain monomers and a positively-charged amino acid into the C H 3 domain of the other of said Fc domain monomers, wherein said negatively-charged amino acid and said positively-charged amino acid are positioned to promote formation of an Fc domain. dimerization selectivity modules comprising an engineered cavity into the C H 3 domain of one of said Fc domain monomers and an engineered protuberance into the C H 3 domain of the other of said Fc domain monomers, wherein said engineered cavity and said engineered protuberance are positioned to form a protuberance-into-cavity pair of Fc domain monomers; and dimerization selectivity modules comprising a negatively-charged amino acid into the C H 3 domain of one of said domain monomers and a positively-charged amino acid into the C H 3 domain of the other of said Fc domain monomers, wherein said negatively-charged amino acid and said positively-charged amino acid are positioned to promote formation of an Fc domain.