Chimeric antigen receptor (CAR)-T cell therapy has recently been introduced as a promising therapeutic T cell-based therapy. Autologous T cells are collected from the patient, engineered in vitro to express artificial chimeric receptors against a specific tumor antigen, and infused into the patient. The success of adoptive CAR-T cells for cancer immunotherapies, particularly in hematological malignancies, inspired researchers of the field. These armored T cells also showed a great potential to be used in the treatment of pediatric brain tumors and autoimmune diseases. In this chapter, we summarize the basics and developments of CAR-T cells from our previous review articles and then discuss the current progress in the pre-clinical and clinical application of CAR-T cells in brain tumors and autoimmune diseases.