Since the arrival of the Internet there have been numerous attempts to create digital money. However, none was successful until Bitcoin appeared in 2009. This has resulted in an explosion of innovation, both in Bitcoin itself, its emulators, and in more functionally rich forms of cryptocurrency. Many such 'coins' will disappear, but a few, most notably Bitcoin, Ethereum and Solana, are likely to survive and even thrive. We will describe how Bitcoin enables electronic transfer of value directly between peers. We also discuss 'smart' cryptos such as Ethereum, which enable much richer functionality such as stablecoins and decentralised finance. Crypto has its drawbacks, such as energy usage, volatility, money laundering and scams. Is crypto really 'Rat poison squared' (Warren Buffet, 2018), a ponzi scheme, or the future of digital money? No intrinsic knowledge is assumed, just an interest in the burgeoning digital economy. No investment recommendations will be made.