To develop into full-blown, metastatic malignancies, primary tumors typically evolve over years to thwart immune attack. Tumor immunology identifies and describes those defenses, while immunotherapy seeks to undo them to revive or direct an immune assault on cancer. Ludwig researchers have for decades made seminal discoveries in both those efforts, identifying the first known naturally occurring tumor antigens, providing the first evidence of tumor escape from immune surveillance and bringing the first generation of immunotherapies to the clinic. They continue today to expand on those proud accomplishments in laboratories around the world. Tumor immunology at Ludwig runs the gamut—from the basic immunology of suppressive immune cells harnessed by tumors and the identification of novel mechanisms of immunosuppression all the way to the development of general and personalized therapies to dismantle those defenses and treat cancer.