Disulfiram (DSF), a derivative of thiuram, has been used in humans to treat alcoholism for more than 60 years. Over the past decade, however, increasing evidence indicates that DSF possesses a great potential for the treatment of human cancers. DSF’s anticancer activity has been demonstrated in both in vitro and in vivo model systems, and has been tested in human clinical trials for various cancer types. It is also evident that DSF can sensitize tumor cells to radiotherapy and enhance the cytotoxicity of anticancer drugs, thus DSF may serve as an adjuvant therapy. The key to DSF’s anticancer action relates to its ability to suppress cancer stem cells by targeting aldehyde dehydrogenase (ALDH), a marker of cancer stem cells, and inhibit proteasome activity in cancer cells by forming complexes with metal ions. In addition, DSF targets epigenetic mechanisms and modulates cellular signaling pathways to slow down tumor progression. DSF also induces apoptosis, inhibits cancer cell proliferation, and suppresses cancer cell metastasis. Considering that the pharmacokinetics of DSF are well-established and a safety profile has been recorded, this compound is an attractive “old” drug that has great potential for rapid development into a new cancer therapeutic. This article provides a brief review of the history of DSF use in humans, evidence for its anticancer activities, the molecular mechanisms of DSF action that have been illustrated by recent studies, and the potential for repurposing DSF as a new chemotherapeutic drug in the near future.