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 to express smart contracts, with two specific characteristics: 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 implementation (in OCaml) that took into account safety and security from the very beginning, and in particular the use of static typing and formal methods when possible. For example, Michelson, the smart contract language of 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. 1 Context A crypto-ledger is an append-only distributed data structure, with a consensus mechanism to avoid inconsistencies in the view of the most up-to-date version. It is also often called a Blockchain, popularized by the Bitcoin crypto-currency, and the tens of new crypto-currencies appearing every year. Among them, Ethereum was probably the most innovative one (and the main challenger for Bitcoin), with an expressive language to write smart contracts, i.e. programs that are executed when they are added to the blockchain or when they are called by other contracts. However, Ethereum is also famous for the hack of the TheDAO smart contract, on June 17, 2016, when an attacker stole around 50 Million dollars of Ether in a few minutes, using a known vulnerability in the smart contract code. Following this attack, the blockchain was updated to remove the attack, but the update was followed by only 85% of the miners, leading to a fork of the network in two separate networks, Ethereum and Ethereum classic. 2 The Tezos project The Tezos project was started in 2014, with the publication of a white paper on a self-amending crypto-ledger[1]. The paper showed, well before fork of Ethereum, the importance of governance in a crypto-ledger, and proposed a mechanism to avoid forks of the network.