Because cancer is one of the leading causes of death worldwide, intensive efforts are being made to discover new types of therapy. Immunotherapy represents a new and modern approach in the treatment of cancer, infectious diseases, and autoimmune diseases. It shows promising results especially in the treatment of malignant formations. Unlike traditional therapies (chemotherapy and radiotherapy), it achieves an effective reaction and response to tumors by directly acting on the immune system, making it safer and less harmful to patients. It is divided into several significant areas: cellular immunotherapy, antibody immunotherapy, checkpoint inhibitors, cytokine therapy, immunomodulators, and vaccines. Due to its remarkable results in clinical trials and the fact that several therapies have already been approved by the FDA, I have decided to focus more on cellular immunotherapy, especially on CAR-T cells. Cellular immunotherapy has experienced a significant breakthrough and forms the foundation for the future cancer treatments. It is based on enhancing the functions of immune cells through their modification, multiplication, and activation, and it is categorized based on the type of cell whose function is being improved. We distinguish between adoptive T cell (TILs, CAR-T, TCR-T), NK cell, CIK cell immunotherapy, and DC vaccines. The most significant type of therapy is adoptive T cell immunotherapy. It shows exceptionally good results in cancer treatment, and due to intensive and dedicated work, a series of therapies of this kind have already been approved.