For over the last hundred years, the scientific community has demonstrated much interest in the roles of the immune system in regulating tumor progression. Extensive research that was performed in this context has revealed that mechanisms of acquired immunity can be highly potent in eradicating cancer cells, if given the right conditions to do so. Basic and clinical studies have paved the way toward the design of sophisticated modalities that improve the ability of T cells to efficiently recognize cancer antigens (when expressed by the tumor cells) and to expand thereafter; alongside developing procedures that prevent immune suppression caused by inhibitory immune checkpoints, these approaches offer cancer patients improved immunotherapies, which increase remission and prolong survival. The current chapter provides a summary of key aspects relevant to such immunotherapies, including the following: (1) cancer vaccines that enhance cancer antigen presentation; (2) adoptive cell transfer (ACT)-based therapies, like tumor-infiltrating lymphocytes (TILs) and chimeric antigen receptor expressing T cells (CAR-T cells); and (3) immune checkpoint blockades (ICBs) that downregulate the extent of immune suppression mediated by inhibitory immune checkpoint molecules, like cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1) and its ligands, primarily PD-L1 (and also PD-L2). These treatments have revolutionized the immunotherapy field, demonstrating the strong power of acquired immunity in preventing tumor growth and progression, giving much hope to cancer patients worldwide.