This book mainly introduces that when immunologic agents act on the checkpoint proteins on cell surfaces, the immune system detects and destroys cancer cells so that a wide range of chemotherapy-refractory malignant tumors can be effectively treated. Because of the distinctive features of immunotherapy of cancer and the rapid progress made in the field, clinical guidance is needed on the use of these agents, including selection of appropriate patient, sequencing of treatment, reaction monitoring, adverse event management, and biomarker testing.