Tumor treating fields (TTFs) are an evolving new anticancer modality. The U.S. Food and Drug Administration has approved the first device, the NovoTTF-100A™, that uses this technology and is indicated for use in progressive glioblastoma multiforme after standard therapies have failed. Promising clinical trial results will likely lead to expanded uses in primary brain tumors and other cancer types. This article will review the concept of TTFs and their mechanism of action, and overview the TTF device and its approved usage.