Peptides have emerged as novel and promising medicaments for the treatment of many human diseases, including tumors. In the treatment of cancer, they can be employed directly as bioactive therapeutics, promoting the reduction of tumor growth, but also as drug delivery systems, to facilitate the passage of drugs through cell and tissue barriers and to increase the selectivity of therapeutics for tumor cells. The advantages of peptides over standard chemotherapeutic agents are several-fold and include ease of synthesis, high efficacy, reduced side-effects, and low production cost. Numerous preclinical evaluations with different types of peptides have provided promising results in murine brain tumor models. Some of the most effective molecules were translated into clinical trials, opening new perspectives for the treatment of high-grade brain tumors and metastases.