This document discusses the basic principles of immunotherapy. It describes how the immune system can recognize and kill cancer cells through immune editing and different types of immunotherapy including cancer vaccines, adoptive cell therapies using CAR T cells or TILs, and immunomodulation using checkpoint inhibitors or bispecific T cell engagers. Effective cancer vaccines require delivering antigens to dendritic cells to activate antigen-specific T cells, but tumors can develop escape mechanisms. Adoptive cell therapies aim to overcome tolerance by introducing external T cells while checkpoint inhibitors enhance endogenous immune responses. Combination approaches may improve outcomes over single agent immunotherapies.