Blockchains are a remarkably transparent and decentralised way of recording lists of transactions. Their best-known use is for digital currencies such as Bitcoin, which announced blockchain technology to the world with a headline-grabbing 1000% increase in value in the course of a single month in 2013. This bubble quickly burst, but steady growth since 2015 means Bitcoins are currently valued higher than ever before.
There are many different ways of using blockchains to create new currencies. Hundreds of such currencies have been created with different features and aims. The way blockchain-based currency transactions create fast, cheap and secure public records means that they also can be used for many non-financial tasks, such as casting votes in elections or proving that a document existed at a specific time. Blockchains are particularly well suited to situations where it is necessary to know ownership histories. For example, they could help manage supply chains better, to offer certainty that diamonds are ethically sourced, that clothes are not made in sweatshops and that champagne comes from Champagne. They could help finally resolve the problem of music and video piracy, while enabling digital media to be legitimately bought, sold, inherited and given away second-hand like books, vinyl and video tapes. They also present opportunities in all kinds of public services such as health and welfare payments and, at the frontier of blockchain development, are self-executing contracts paving the way for companies that run themselves without human intervention (Fig. \ref{146340}).