A bispecific antibody specifically binding to HER2 comprising a first antigen binding site specific for extracellular domain II of HER2 and a second antigen binding site specific for extracellular domain IV of HER2, wherein the bispecific antibody is monovalent for both the extracellular domain II and IV of HER2, wherein the bispecific antibody comprises (i) a first heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 55; (b) a heavy chain CDR2 of SEQ ID NO: 77; (c) a heavy chain CDR3 of SEQ ID NO: 56; and a second heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 20; (b) a heavy chain CDR2 of SEQ ID NO: 29; (c) a heavy chain CDR3 of SEQ ID NO: 30; and a first and a second light chain comprising (a) a light chain CDR1 of SEQ ID NO: 89; (b) a light chain CDR2 of SEQ ID NO: 90; (c) a light chain CDR3 of SEQ ID NO: 19; (ii) a first heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 14; (b) a heavy chain CDR2 of SEQ ID NO: 60; (c) a heavy chain CDR3 of SEQ ID NO: 16; and a second heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 20; (b) a heavy chain CDR2 of SEQ ID NO: 29; (c) a heavy chain CDR3 of SEQ ID NO: 30; and a first and a second light chain comprising (a) a light chain CDR1 of SEQ ID NO: 89; (b) a light chain CDR2 of SEQ ID NO: 90; (c) a light chain CDR3 of SEQ ID NO: 19; or (iii) a first heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 58; (b) a heavy chain CDR2 of SEQ ID NO: 15; (c) a heavy chain CDR3 of SEQ ID NO: 59; and a second heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 20; (b) a heavy chain CDR2 of SEQ ID NO: 29; (c) a heavy chain CDR3 of SEQ ID NO: 30; and a first and a second light chain comprising (a) a light chain CDR1 of SEQ ID NO: 89; (b) a light chain CDR2 of SEQ ID NO: 90; (c) a light chain CDR3 of SEQ ID NO: 19. (i) a first heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 55; (b) a heavy chain CDR2 of SEQ ID NO: 77; (c) a heavy chain CDR3 of SEQ ID NO: 56; and a second heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 20; (b) a heavy chain CDR2 of SEQ ID NO: 29; (c) a heavy chain CDR3 of SEQ ID NO: 30; and a first and a second light chain comprising (a) a light chain CDR1 of SEQ ID NO: 89; (b) a light chain CDR2 of SEQ ID NO: 90; (c) a light chain CDR3 of SEQ ID NO: 19; (a) a heavy chain CDR1 of SEQ ID NO: 55; (b) a heavy chain CDR2 of SEQ ID NO: 77; (c) a heavy chain CDR3 of SEQ ID NO: 56; (a) a heavy chain CDR1 of SEQ ID NO: 20; (b) a heavy chain CDR2 of SEQ ID NO: 29; (c) a heavy chain CDR3 of SEQ ID NO: 30; (a) a light chain CDR1 of SEQ ID NO: 89; (b) a light chain CDR2 of SEQ ID NO: 90; (c) a light chain CDR3 of SEQ ID NO: 19; (ii) a first heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 14; (b) a heavy chain CDR2 of SEQ ID NO: 60; (c) a heavy chain CDR3 of SEQ ID NO: 16; and a second heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 20; (b) a heavy chain CDR2 of SEQ ID NO: 29; (c) a heavy chain CDR3 of SEQ ID NO: 30; and a first and a second light chain comprising (a) a light chain CDR1 of SEQ ID NO: 89; (b) a light chain CDR2 of SEQ ID NO: 90; (c) a light chain CDR3 of SEQ ID NO: 19; or (a) a heavy chain CDR1 of SEQ ID NO: 14; (b) a heavy chain CDR2 of SEQ ID NO: 60; (c) a heavy chain CDR3 of SEQ ID NO: 16; (a) a heavy chain CDR1 of SEQ ID NO: 20; (b) a heavy chain CDR2 of SEQ ID NO: 29; (c) a heavy chain CDR3 of SEQ ID NO: 30; (a) a light chain CDR1 of SEQ ID NO: 89; (b) a light chain CDR2 of SEQ ID NO: 90; (c) a light chain CDR3 of SEQ ID NO: 19; or (iii) a first heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 58; (b) a heavy chain CDR2 of SEQ ID NO: 15; (c) a heavy chain CDR3 of SEQ ID NO: 59; and a second heavy chain comprising (a) a heavy chain CDR1 of SEQ ID NO: 20; (b) a heavy chain CDR2 of SEQ ID NO: 29; (c) a heavy chain CDR3 of SEQ ID NO: 30; and a first and a second light chain comprising (a) a light chain CDR1 of SEQ ID NO: 89; (b) a light chain CDR2 of SEQ ID NO: 90; (c) a light chain CDR3 of SEQ ID NO: 19. (a) a heavy chain CDR1 of SEQ ID NO: 58; (b) a heavy chain CDR2 of SEQ ID NO: 15; (c) a heavy chain CDR3 of SEQ ID NO: 59; (a) a heavy chain CDR1 of SEQ ID NO: 20; (b) a heavy chain CDR2 of SEQ ID NO: 29; (c) a heavy chain CDR3 of SEQ ID NO: 30; (a) a light chain CDR1 of SEQ ID NO: 89; (b) a light chain CDR2 of SEQ ID NO: 90; (c) a light chain CDR3 of SEQ ID NO: 19.