Bitcoin can be considered as a medium exchange restricted to online markets, it is not aunit of account and a store of value, and thus cannot be considered as a money. Bitcoinvalue is very volatile and traded for different prices in different exchanges platforms,and thus can be used for arbitrage purpose. His behavior can be associated with ahigh volatile stock, and most transactions in Bicoin are aimed to speculative instruments. The high volatility in Bitcoin and the occurrence of speculative bubble dependon positive sentiment and confidence about Bitcoin market: several variables my beconsidered as indicators (volume of transactions, number of transactions, number ofGoogle research, wikipedia requests). The star of the crypto-currencies has attainedthe 19 716 dollars in December 2017 and decreased to 6707 dollars March 29, 2018. Incapitalization is at this time the 30th mondial currency. We explain some limits andinterests of the Bitcoin system and why the central bankers and regulators need totake some decision on its existence, and in a second paper we suggest what could bethe possible evolution of the Bitcoin Blockchain.