The paper discusses various issues related to both theory and practice of the world of digital currencies. The growing popularity of the sector of services based on the technology of a distributed ledger, called decentralized finance (DeFi), is considered in detail, which has grown over the last year from 700 million to 11.5 billion US dollars. Different analogs of traditional financial and banking services are being built in this sector, in which, instead of the corresponding institutions, there is a set of smart contracts operating in an automatic mode. In addition, the paper analyzes the theoretical risks and potential benefits from the emission of digital currencies by central banks, and considers the world experience of the pilot projects of digital currencies in different countries.