A bispecific Fc (Bi-Fc) polypeptide, which is monomeric and comprises (a) a polypeptide chain comprising an amino acid sequence having the following formula: V1-L1-V2-L2-V3-L3-V4-L4-Fc; wherein Fc is a human IgG Fc polypeptide chain which is C-terminal relative to the four immunoglobulin variable regions; wherein two of V1, V2, V3, and V4 are immunoglobulin heavy chain variable regions and the other two are immunoglobulin light chain variable regions; wherein either V1 is a VH region and V2 is a VL region or vice versa and either V3 is a VH region and V4 is a VL region or vice versa; wherein L1, L2, L3, and L4 are linkers, wherein L2 is present and wherein L2 is not more than 12 amino acids long; wherein L1 and L3 are each at least 15 amino acids long; and wherein L4 can be present or absent; or (b) a polypeptide chain comprising an amino acid sequence having the following formula: Fc-L4-V1-L1-V2-L2-V3-L3-V4; wherein Fc is a human IgG Fc polypeptide chain which is N-terminal relative to the four immunoglobulin variable regions; wherein either V1 is a VH region and V2 is a VL region or vice versa and either V3 is a VH region and V4 is a VL region or vice versa; wherein two of V1, V2, V3, and V4 are VH regions and the other two are VL regions; wherein L1, L2, L3, and L4 are linkers, wherein L2 is present and wherein L2 is not more than 12 amino acids long; wherein L1 and L3 are each at least 15 amino acids long; and wherein L4 can be present or absent; wherein the Bi-Fc binds to a target cell and an immune effector cell and/or mediates cytolysis of a target cell by an immune effector cell, wherein the polypeptide chain targeting the effector cell binds to human and/or cynomolgus CD3ε, wherein the Fc polypeptide chain of the Bi-Fc comprises an insertion of the amino acid sequence of any of SEQ ID NOs:36-47 between positions 384 and 385, wherein these position numbers are assigned according to the EU numbering scheme. (a) a polypeptide chain comprising an amino acid sequence having the following formula: V1-L1-V2-L2-V3-L3-V4-L4-Fc; wherein Fc is a human IgG Fc polypeptide chain which is C-terminal relative to the four immunoglobulin variable regions; wherein two of V1, V2, V3, and V4 are immunoglobulin heavy chain variable regions and the other two are immunoglobulin light chain variable regions; wherein either V1 is a VH region and V2 is a VL region or vice versa and either V3 is a VH region and V4 is a VL region or vice versa; wherein L1, L2, L3, and L4 are linkers, wherein L2 is present and wherein L2 is not more than 12 amino acids long; wherein L1 and L3 are each at least 15 amino acids long; and wherein L4 can be present or absent; or wherein two of V1, V2, V3, and V4 are immunoglobulin heavy chain variable regions and the other two are immunoglobulin light chain variable regions; wherein either V1 is a VH region and V2 is a VL region or vice versa and either V3 is a VH region and V4 is a VL region or vice versa; wherein L1, L2, L3, and L4 are linkers, wherein L2 is present and wherein L2 is not more than 12 amino acids long; wherein L1 and L3 are each at least 15 amino acids long; and wherein L4 can be present or absent; or (b) a polypeptide chain comprising an amino acid sequence having the following formula: Fc-L4-V1-L1-V2-L2-V3-L3-V4; wherein Fc is a human IgG Fc polypeptide chain which is N-terminal relative to the four immunoglobulin variable regions; wherein either V1 is a VH region and V2 is a VL region or vice versa and either V3 is a VH region and V4 is a VL region or vice versa; wherein two of V1, V2, V3, and V4 are VH regions and the other two are VL regions; wherein L1, L2, L3, and L4 are linkers, wherein L2 is present and wherein L2 is not more than 12 amino acids long; wherein L1 and L3 are each at least 15 amino acids long; and wherein L4 can be present or absent; wherein either V1 is a VH region and V2 is a VL region or vice versa and either V3 is a VH region and V4 is a VL region or vice versa; wherein two of V1, V2, V3, and V4 are VH regions and the other two are VL regions; wherein L1, L2, L3, and L4 are linkers, wherein L2 is present and wherein L2 is not more than 12 amino acids long; wherein L1 and L3 are each at least 15 amino acids long; and wherein L4 can be present or absent; wherein the Bi-Fc binds to a target cell and an immune effector cell and/or mediates cytolysis of a target cell by an immune effector cell, wherein the polypeptide chain targeting the effector cell binds to human and/or cynomolgus CD3ε, wherein the Fc polypeptide chain of the Bi-Fc comprises an insertion of the amino acid sequence of any of SEQ ID NOs:36-47 between positions 384 and 385, wherein these position numbers are assigned according to the EU numbering scheme.