Interest in cryptocurrencies – one may accurately say, fascination with them – and the decentralized ledger structure supporting them known as the blockchain has accelerated at an astonishing pace in the last year, indeed in just the last six months. Furthermore, the new fundraising mechanism, the initial coin offering or ICO, being used to fund projects to create decentralized apps based on distributed ledger technology has now raised a much larger sum of money than the more than $2 billion that had already been invested by venture capital firms. This talk will explain in layman’s terms what a cryptocurrency is, how the blockchain works, and how the two interact to create an unhackable, decentralized transaction-intermediation system that requires no trusted central intermediating authority, only a multiplicity of uncertified distributed nodes that reach a consensus through a so-called mining process. It will explain how ICOs work, providing examples of legitimately useful ICOs, as opposed to scam ICOs, which are abundant. The talk will speculate on the arguably rational expectations for the future that could explain why the prices of bitcoin and other major cryptocurrencies may not be merely a bubble phenomenon.