Book excerpt: Now, it its second edition, this book summarizes the role of immune cells in tumor suppression and progression. It describes in detail why tumor cells can survive and spread in spite of the antitumor response of immune cells. Since immunotherapy is an attractive approach to cancer therapy, this book also provides information on the two main strategies: monoclonal antibodies and adaptive T cell immunotherapy, with a focus on recent human clinical trials. A newly added chapter also focuses on the role of Natural Killer cells in tumor progression. The book provides a state-of-the-art, comprehensive overview of immune cells in cancer and is an indispensable resource for researchers and practitioners working or lecturing in the field of cancer research and immunology.