The blockchain is a relatively new technology used to verify and store transaction records for online cryptocurrencies like Bitcoin. The system is redundant and distributed, making it difficult for transactions to be rescinded, duplicated, or faked. Beyond online currencies, the blockchain has potential uses in health care, education, and many other fields. This column will briefly describe what the blockchain is and how it is being used, potential future uses that may be of interest to librarians and medical practitioners, and some of the problems with the system.