Despite gradual progress, treatment of most types of cancer today remains woefully inadequate. New approaches are desperately needed to enhance and replace surgery, radiotherapy and chemotherapy, which are the three current therapeutic major options. Cancer immunotherapy is one area of great promise. The progression of cancer, from tumor initiation through disease development and on to the success or failure of therapy, is the outcome of a complex interplay between the host immune system and the tumor. This match up is, literally, a matter of life and death. Scientists working on cancer immunotherapy are aiming to generate anti-tumor responses while overcoming tumor strategies to nullify the immune system. Immunotherapy can take the form of peptide vaccination, monoclonal antibody treatment, dendritic cell vaccination, adoptive cell transfer and other strategies. Much of the work is still in the experimental stage but the U.S. Food and Drug Administration (FDA) has approved two cancer immunotherapeutic agents, namely sipuleucel-T (an autologous cell therapy) and ipilimumab (a monoclonal antibody), for the treatment of prostate cancer and melanoma, respectively. The volume of literature on cancer immunotherapy is enormous. For example, a search for “ cancer immunotherapy ” using the Open Access filter on PubMedCentral generates a list of almost 15,000 articles, including 2400 published in 2014, 3000 in 2013 and over 1800 in 2012. This ScienceOpen Collection in Cancer Immunotherapy is intended to help researchers to stay abreast of this fast-moving field. As a first step, we present a selection of 25 notable papers from the thousand or so published in Open Access format over the second half of 2014 and in January 2015. These were selected to illustrate the breadth and promise of the field, but also the challenges that it faces. They are excellent articles but I make no claim on whether they are the most significant papers published in the field over the period. To develop the Collection as a useful resource for everyone with an interest in cancer immunotherapy, we invite interested researchers to participate by adding their viewpoint on these papers; to take an active role in selecting papers for discussion as they are published; and to use this forum to discuss ideas, topics and issues that might shape the direction for cancer immunotherapy. To become a Collection Editor yourself, please read this information and then apply to Sebastian Alers , Senior Editor.