A company register is a centrepiece of the legal existence of firms in a given country. Usually, these registers are state-controlled. Can we conceive a register that is decentralised? We will present OpenGreffe, an Ethereum-based register based on simple legal foundations of the French Code Civil. What is OpenGreffe? It's a public blockchain-based registry of firms, in the sense of "société de fait" of the Art. 1832 of the French Code Civil. This registry open but is maintained by selected agents, based on reputation. To kickstart reputation: we can base it on existing real-world business reputation. Each entry in the registry is consisting of: a company identification (name, associates, capital) an Ethereum address owned by the associates a stamp of approval by a registry maintainer a date. The goal: make it possible for anyone to register a company and build reputation for it in the Ethereum world, so as to raise funding, loans, use insurance, etc. Lifecycle of a registration Some founders agree on starting the business. They share an Ethereum address on a multi-sig wallet. They go see some 2+ existing registry maintainers (like Legalstart plus another lawyer company), and ask them to perform KYC/KYB to verify that capital is well shared and that they indeed aim to work together on some projects. The registry maintainers commit the change to the OpenGreffe database. The founders can start building their Ethereum-based business, using the Ethereum address that has been written in the registry. After some months/years, for example some external auditors (like Euler-Hermes, an insurance company) can start scoring the new company for their credit defaults and account payables. Good news: they give an AAA rating, because the founders did well! After some more time, when the founders want to raise a loan, they can claim being proper on their credit payments thanks to external auditors! All of this, without the use of any state institution! Notes: step 6 is possible thanks to OpenGreffe only. Indeed, without the registry, good account payables behavior on a given Ethereum address couldn't be linked to a company identification. Question TBD: why do we need anything other than an Ethereum address? Why identify associates and a company name...?