The tumour antigen ErbB-2 belongs to the epidermal growth factor receptor family. Numerous studies have shown that ErbB-2 is overexpressed in many cancers and it is prognostically important in a subset of malignancies. It is well recognised that this receptor has many characteristics that make it an excellent target for tumour-specific immunotherapy. One anti-ErbB-2 monoclonal antibody, Herceptin or TrastuzuMab, has already shown clinical efficacy for the treatment of metastatic breast cancer. However, despite this success, it is still currently unclear how monoclonal antibodies inhibit tumour growth in vivo. This review will summarise the biological activities of a range of anti-ErbB-2 Mabs, as well as their possible mechanisms of action. In addition, as an active mode of immunotherapy, the current vaccine strategies for inducing or enhancing ErbB-2-specific immunity will also be discussed. It is anticipated that a better understanding of the activities of anti-ErbB-2 Mabs will aid in the development of both passive and active immunotherapies against this important receptor.