The present invention concerns isolated antibodies that specifically bind to the human ErbB4 of SEQ ID NO:2, as well as humanized antibodies, human antibodies and antibody fragments, as well as bispecific antibodies capable of binding both the human ErbB4 of SEQ ID NO:2 and ErbB3. The invention further concerns antibodies which specifically bind to human ErbB4 of SEQ ID NO: 2 with a Kd less than 100 nM, antibodies which specifically bind to human ErbB4 of SEQ ID NO: 2 and which reduces heregulin binding thereto, and antibodies which specifically bind to human ErbB4 of SEQ ID NO: 2 and which reduce heregulin-induced tyrosine phosphorylation thereof.