Cancer immunotherapy was announced as the "Breakthrough of the Year 2013" by Science Magazine (December 2013), but there is still a lot of uncertainty in how to design and deliver therapies that boost the immune system’s defense against cancer. In this talk, I will present a brief overview of cancer immunotherapies, including therapeutic cancer vaccines. I will briefly discuss nonspecific and specific immunotherapies, their uses and their drawbacks. I will also highlight how mathematical modeling has been used to understand the effects of immunotherapies, and to design treatment strategies. Most of these models address one of the two main treatment design questions: How Much? and How Often?