A bispecific antibody comprising an Fc region and a Fab region, wherein: (i) said Fc region comprises two non-identical heavy chains, wherein at least one of said two non-identical heavy chains comprises an amino acid modification so as to form a steric complementation between said two non-identical heavy chains, wherein said Fc region comprises a protuberance of one heavy chain of said Fc region and a sterically compensatory cavity on a second heavy chain of said Fc region, said protuberance protruding into said compensatory cavity, wherein said complementation is generated by: (a) substituting an amino acid at one position on a CH3 domain of said one heavy chain with another amino acid having a larger side chain volume than the original amino acid, said amino acid having a larger side chain being selected from the group consisting of tyrosine, arginine, phenylalanine, isoleucine and tryptophan so as to generate said protuberance; and (b) substituting an amino acid at one position on a CH3 domain of said second heavy chain with another amino acid having a smaller side chain volume than the original amino acid so as to generate said compensatory cavity, said amino acid having a smaller side chain being selected from the group consisting of alanine, glycine, valine and threonine; and (ii) said Fab region comprises a first covalent link between a first heavy chain and a first light chain of said Fab region and a second covalent link between a second heavy chain and a second light chain of said Fab region, wherein said first covalent link is a naturally occurring disulfide bond between a CH1 domain of said one heavy chain and a CL domain of said one light chain; and said second covalent link is a disulfide bond between a cysteine at position 44 of a V H domain of said second heavy chain and a cysteine at position 100 of a V L domain of said second light chain, wherein the numbering of said position is according to Kabat and Wu, wherein said second heavy chain is devoid of its native disulfide bond with said second light chain, said native disulfide bond being an interchain disulfide bond that connects a heavy chain to its cognate light chain encoded in a naturally occurring germline antibody gene. (i) said Fc region comprises two non-identical heavy chains, wherein at least one of said two non-identical heavy chains comprises an amino acid modification so as to form a steric complementation between said two non-identical heavy chains, wherein said Fc region comprises a protuberance of one heavy chain of said Fc region and a sterically compensatory cavity on a second heavy chain of said Fc region, said protuberance protruding into said compensatory cavity, wherein said complementation is generated by: (a) substituting an amino acid at one position on a CH3 domain of said one heavy chain with another amino acid having a larger side chain volume than the original amino acid, said amino acid having a larger side chain being selected from the group consisting of tyrosine, arginine, phenylalanine, isoleucine and tryptophan so as to generate said protuberance; and (b) substituting an amino acid at one position on a CH3 domain of said second heavy chain with another amino acid having a smaller side chain volume than the original amino acid so as to generate said compensatory cavity, said amino acid having a smaller side chain being selected from the group consisting of alanine, glycine, valine and threonine; and (a) substituting an amino acid at one position on a CH3 domain of said one heavy chain with another amino acid having a larger side chain volume than the original amino acid, said amino acid having a larger side chain being selected from the group consisting of tyrosine, arginine, phenylalanine, isoleucine and tryptophan so as to generate said protuberance; and (b) substituting an amino acid at one position on a CH3 domain of said second heavy chain with another amino acid having a smaller side chain volume than the original amino acid so as to generate said compensatory cavity, said amino acid having a smaller side chain being selected from the group consisting of alanine, glycine, valine and threonine; and (ii) said Fab region comprises a first covalent link between a first heavy chain and a first light chain of said Fab region and a second covalent link between a second heavy chain and a second light chain of said Fab region, wherein said first covalent link is a naturally occurring disulfide bond between a CH1 domain of said one heavy chain and a CL domain of said one light chain; and said second covalent link is a disulfide bond between a cysteine at position 44 of a V H domain of said second heavy chain and a cysteine at position 100 of a V L domain of said second light chain, wherein the numbering of said position is according to Kabat and Wu, wherein said second heavy chain is devoid of its native disulfide bond with said second light chain, said native disulfide bond being an interchain disulfide bond that connects a heavy chain to its cognate light chain encoded in a naturally occurring germline antibody gene.