The emergence of virtual currencies, based on cryptographic protocols, raises questions about their status. Here, we analyze the case of Bitcoin. We show that bitcoin does not fulfil the traditional functions of money. Acceptability as a means of payment is limited. Its volatility is too high to serve as store of value. And bitcoin is not used as a unit of account. However, as a collaborative and decentralized technology, the blockchain, used to issue the currency and settle transactions has the potential to change the centralized organization of payment and settlement system.