In this talk, we will present the story of the Tezos project. Tezos is a crypto-ledger, i.e. a distributed blockchain with a language for smart contracts, with two specific character- istics: the first one is its ability for self-amendment, that allows a majority of stake-holders to update the behavior of Tezos without risking a fork; the second one is a design and im- plementation (in OCaml) that took into account safety and security from the beginning, and in particular the use of static typing and formal methods when possible. For example, Michelson, the language for smart contracts in Tezos, is the only such language with a formal semantics, a type system ensuring no runtime errors, and an implementation that uses OCaml GADTs to ensure its correctness.