Alternating electric fields therapy, as delivered by the tumor treating fields device, is a new modality of cancer treatment that has been approved by the US FDA for recurrent glioblastoma. At a frequency of 200 kHz, these fields emanate from transducer arrays on the surface of the patient’s scalp into the brain and perturb processes necessary for cytokinesis during tumor cell mitosis. In the registration Phase III trial for recurrent glioblastoma patients, the efficacy of the tumor treating fields as monotherapy was equivalent to chemotherapy, while scalp irritation was its major adverse event compared with systemic toxicities that were associated with cytotoxic chemotherapies. Alternating electric fields therapy is, therefore, an essential option for the treatment of recurrent glioblastoma. Here, we summarize our current knowledge of the physics, cell biology and clinical data supporting the use of the tumor treating fields therapy.