Anticancer active immunotherapy embodies the ideal antitumor therapy, as it theoretically combines target specificity with long-term disease control. Peptide-based cancer vaccines represent the most specific approach to polarize the immune system against malignant cells, since they are preparations made of single epitopes, the minimal immunogenic region of an antigen. Despite the strong rational, the promising preclinical results and the frequent induction of antigen-specific immune responses, peptide-based cancer vaccines have yielded relatively poor results in the clinical setting, a phenomenon likely due to the immunosuppressive properties of the tumor microenvironment that allow malignant cells to evade both naturally occurring and therapeutically induced immune surveillance. Nevertheless, advances in the engineering of peptides and in our understanding of the molecular mechanisms underlying an effective immune response against tumors have renewed the enthusiasm for peptide-based vaccination regimens in the setting of cancer, and a variety of clinical trials are being conducted based on the use of peptides. This review will describe the most recent insights in the rational design of peptide-based cancer vaccines, as well as the challenges to successful anticancer immunotherapy based on these short amino acid chains.