Abstract: Blockchain, a continuously growing tamper resistant data structure, was developed as the technology underlying the Bitcoin crypto-currency and it is now being applied to a wide range of problems as a form of ‘Distributed Ledger’. The promise of this technology has been recognised by governments and the financial industry. It also has application to enhance privacy of personal information, to secure the Internet of things and to change electronic identity. This study explains what a Blockchain is and how it works. It describes some actual and the potential applications of this technology together with some of the risks associated with its use.