Bitcoin is the first decentralized cryptocurrency. It can be sent from one person to another over the Bitcoin network in a peer-to-peer manner without the need for a third party. Transactions on the network are verified using cryptography and recorded in a distributed ledger called the blockchain without a central authority overseeing it. Consensus among nodes is achieved through an intensive computational process known as proof of work, which secures Bitcoin's blockchain. Mining consumes large amounts of electricity and has been criticized for Bitcoin's environmental impact.