The recent development for crypto-assets make the interest on blockchain technology growing. To understand the interest of this innovation for the economy and the finance, it is important to study the basements of the concept around the technology blockchain. First, we will introduce the notion of peer-topeer lending which is one of the component of the question, and then we will explain the concept of Bitcoin which is the first crypto-asset which has been developed based on a PoW (Proof-of-work) protocol. We will analyze at the same time the risks associated to this crypto-asset and the regulation which exists. In a second step, we will present and analyze different classes of blockchains and the mechanisms associated to them. We will introduce the concept of close and open blockchain, public and private. This will permit to introduce the different kinds of protocols which govern these blockchains. Finally, we will introduce the concept of ICO, new way to funds using cryptocurrencies. The analysis of the governance of this new kind of start-up will be provided. The risks associated to these ICO will be analysed and the recent regulation on them provided.