Bitcoin is a strange thing: a virtual coinage, but real enough, each ‘coin’ tethered to a place. If you store bitcoins on your computer and spill coffee on the hard drive, that’s that; when you spend coins online, they travel from your wallet, just as cash physically leaves your pocket. When Mt Gox, a high-profile coin exchange, went out of business in 2014, bitcoins worth half a billion dollars simply disappeared. The bitcoin community hopes the coins will become established as a currency but speculators treat them like a commodity. The US tax authorities, meanwhile, have decided that they are property. In just six years bitcoin has gone from techno-fantasy, through Wild West, to something quite respectable; in Cryptocurrency, their fascinating book on the topic, Wall Street Journal columnists Paul Vigna and Michael Casey set out to convince readers that bitcoin is not only going straight, but also has the potential to change the world.

The most enjoyable parts of Cryptocurrency deal with the extraordinary history of bitcoin. The digital-currency movement has its roots in the ‘cypherpunk’ movement of the 1990s, a grouping of ponytailed hardline libertarian-utopian techno-anarchists, based loosely in the San Francisco Bay area and devoted to freedom, property rights and sound money,