In the past two decades, immunotherapy of cancer has developed into an established treatment option. At first, the development of monoclonal antibodies – targeting overexpressed cell surface molecules on tumour cells – resulted in improved survival when combined with standard chemotherapy or radiotherapy. More recently, T cell immunotherapy has impacted on survival of certain cancer types. In melanoma especially, but now also in renal cell cancer and non-small cell lung cancer, immune checkpoint inhibitors, such as cytotoxic T lymphocyte–associated antigen-4 (anti-CTLA4) and blockade of programmed death receptor-1-PD- ligand 1 (PD1-PD-L1) interaction, represent a completely new treatment paradigm, lowering the threshold for an anticancer immune response and breaking self-tolerance. Adoptive T cell transfer using tumour- infiltrating lymphocytes or genetically modified T cells are under development, but have shown impressive clinical efficacy in several Phase II studies. These emerging but highly promising treatments can give rise to durable tumour control in diseases that were lethal in all patients only a few years ago.