Cancer is the second most common cause of death in Norway. The calculated lifetime risk of developing cancer is 36 % for men and 29 % for women. The traditional cancer therapies surgery, chemotherapy and radiation in many cases are insufficient to cure cancer, with considerable adverse effects. Thus, one has been looking for new therapeutic approaches for cancer. This project thesis reviews current literature concerning cancer immunotherapy, including basic mechanisms in immunology and tumor development as well as clinical studies. Examples of novel immunotherapies, such as antibody based immunotherapy, immune checkpoint inhibitors, chimeric antigen receptor T-cell therapy and cancer vaccines are discussed. The study is based on a nonsystematic literature search in PubMed which includes reviews and original articles. For many years, immunotherapy has been regarded as potentially promising, but also with a degree of skepticism regarding its efficiency. However, recent advances in technology and increased insight into basic immune and cancer immune evasion have changed this. The journal Science highlighted cancer immunotherapy as ”Breakthrough of the Year” for 2013. Although the main purpose of the immune system is to protect against pathogenic microorganisms, it also plays an important role against cancer. Cancer immunotherapy builds upon natural antitumor immune mechanisms, to harness and boost the effects against cancer. Because of its specificity and capacity for memory, immunotherapy against cancer have the potential to achieve complete, long-lasting remissions. Now considered the fourth main therapy against cancer, new immunotherapies are launched at a rapid pace, offering considerable improvements over previous therapies in several types of cancer.