Over the past decade the financial services industry has been disrupted by a range of new technologies. This has included the launch of new, private, digital currencies such as Bitcoin. In this environment, central banks are considering how they can take advantage of these new technologies to help deliver their core functions. This article contributes to this discussion by evaluating the pros and cons of a public digital currency issued by a central bank across four functional areas: currency distribution, payments, monetary stability and financial stability. We distinguish between two kinds of digital currency – ‘conventional’ digital currencies, which rely on existing payments technology to operate, and crypto-currencies which rely on distributed ledged technology (similar to Bitcoin). We find the pros and cons of a central bank issuing a digital currency are mixed across each of the central bank functions, revealing the complexity in evaluating such a currency. In particular, we find the implications for monetary policy and financial stability could be significant, both positively and negatively.