The HER2 receptor is a 185-kDa transmembrane glycoprotein with tyrosine kinase activity, and belongs in the human epidermal growth factor receptor (HER) family consisting of four members. Moreover, aberrant HER2 protein overexpression has been linked to various human gynecological adenocarcinomas, including breast, endometrium, ovary and cervix, and has been found to be a poor prognostic factor for survival. This new book presents topical research in the study of HER2, including targeting HER2 with photodynamic therapy; HER2 shedding as a biomarker in breast cancer; development of trastuzumab resistance and targeted nanomedicines conjugated with HER2 antibodies in cancer therapy.