An isolated monoclonal antibody, wherein the antibody specifically binds to HER3 and comprises: (a) a first V H CDR identical to SEQ ID NO: 15; (b) a second V H CDR identical to SEQ ID NO: 16; (c) a third V H CDR identical to SEQ ID NO: 17; (d) a first V L CDR identical to SEQ ID NO: 18; (e) a second V L CDR identical to SEQ ID NO: 19; and (f) a third V L CDR identical to SEQ ID NO: 20; (a) a first V H CDR identical to SEQ ID NO: 9; (b) a second V H CDR identical to SEQ ID NO: 10; (c) a third V H CDR identical to SEQ ID NO: 11; (d) a first V L CDR identical to SEQ ID NO: 12; (e) a second V L CDR identical to SEQ ID NO: 13; and (f) a third V L CDR identical to SEQ ID NO: 14; (a) a first V H CDR identical to SEQ ID NO: 21; (b) a second V H CDR identical to SEQ ID NO: 22; (c) a third V H CDR identical to SEQ ID NO: 23; (d) a first V L CDR identical to SEQ ID NO: 24; (e) a second V L CDR identical to SEQ ID NO: 25; and (f) a third V L CDR identical to SEQ ID NO: 26; or (a) a first V H CDR identical to SEQ ID NO: 27; (b) a second V H CDR identical to SEQ ID NO: 28; (c) a third V H CDR identical to SEQ ID NO: 29; (d) a first V L CDR identical to SEQ ID NO: 30; (e) a second V L CDR identical to SEQ ID NO: 31; and (f) a third V L CDR identical to SEQ ID NO: 32. (a) a first V H CDR identical to SEQ ID NO: 15; (b) a second V H CDR identical to SEQ ID NO: 16; (c) a third V H CDR identical to SEQ ID NO: 17; (d) a first V L CDR identical to SEQ ID NO: 18; (e) a second V L CDR identical to SEQ ID NO: 19; and (f) a third V L CDR identical to SEQ ID NO: 20; (a) a first V H CDR identical to SEQ ID NO: 15; (b) a second V H CDR identical to SEQ ID NO: 16; (c) a third V H CDR identical to SEQ ID NO: 17; (d) a first V L CDR identical to SEQ ID NO: 18; (e) a second V L CDR identical to SEQ ID NO: 19; and (f) a third V L CDR identical to SEQ ID NO: 20; (a) a first V H CDR identical to SEQ ID NO: 9; (b) a second V H CDR identical to SEQ ID NO: 10; (c) a third V H CDR identical to SEQ ID NO: 11; (d) a first V L CDR identical to SEQ ID NO: 12; (e) a second V L CDR identical to SEQ ID NO: 13; and (f) a third V L CDR identical to SEQ ID NO: 14; (a) a first V H CDR identical to SEQ ID NO: 9; (b) a second V H CDR identical to SEQ ID NO: 10; (c) a third V H CDR identical to SEQ ID NO: 11; (d) a first V L CDR identical to SEQ ID NO: 12; (e) a second V L CDR identical to SEQ ID NO: 13; and (f) a third V L CDR identical to SEQ ID NO: 14; (a) a first V H CDR identical to SEQ ID NO: 21; (b) a second V H CDR identical to SEQ ID NO: 22; (c) a third V H CDR identical to SEQ ID NO: 23; (d) a first V L CDR identical to SEQ ID NO: 24; (e) a second V L CDR identical to SEQ ID NO: 25; and (f) a third V L CDR identical to SEQ ID NO: 26; or (a) a first V H CDR identical to SEQ ID NO: 21; (b) a second V H CDR identical to SEQ ID NO: 22; (c) a third V H CDR identical to SEQ ID NO: 23; (d) a first V L CDR identical to SEQ ID NO: 24; (e) a second V L CDR identical to SEQ ID NO: 25; and (f) a third V L CDR identical to SEQ ID NO: 26; or (a) a first V H CDR identical to SEQ ID NO: 27; (b) a second V H CDR identical to SEQ ID NO: 28; (c) a third V H CDR identical to SEQ ID NO: 29; (d) a first V L CDR identical to SEQ ID NO: 30; (e) a second V L CDR identical to SEQ ID NO: 31; and (f) a third V L CDR identical to SEQ ID NO: 32. (a) a first V H CDR identical to SEQ ID NO: 27; (b) a second V H CDR identical to SEQ ID NO: 28; (c) a third V H CDR identical to SEQ ID NO: 29; (d) a first V L CDR identical to SEQ ID NO: 30; (e) a second V L CDR identical to SEQ ID NO: 31; and (f) a third V L CDR identical to SEQ ID NO: 32.