The underlying premise of tumor immunology is that the immune system is capable of recognizing cancer cells and that immune recognition can lead to rejection of tumors by the host. We focus on recent advances in tumor immunology in experimental systems, including the molecular identification of tumor antigens, studies of recognition of tumor cells by the immune system, and the development of new strategies for treatment of cancer. Identifying potential target antigens on tumors and defining effector arms of the immune system that mediate tumor rejection (including T cells, natural killer cells, antibodies, complement cells, and cytokines) remain crucial problems for the field.