Proof of Work
A blockchain consensus mechanism where miners expend computational effort to earn the right to add the next block.
What is Proof of Work?
Proof of work (PoW) is the original blockchain consensus mechanism, first implemented by Bitcoin. It requires participants ('miners') to compete in solving a computationally expensive cryptographic puzzle — finding a hash output below a target difficulty — before they may add a new block of transactions to the chain. The solution is easy for the network to verify but hard to produce, requiring significant computational effort and energy expenditure. This 'work' creates a credible cost that deters attacks: rewriting a past block would require redoing all the work for that block and every subsequent block, while outpacing the rest of the network. The miner who first finds a valid solution earns newly minted cryptocurrency (the block reward) plus transaction fees. Proof of work's high energy consumption has been cited as an environmental concern, driving the adoption of proof-of-stake alternatives.
Example
Bitcoin's mining difficulty adjusts every 2,016 blocks (approximately two weeks) so that, on average, a valid block is found every 10 minutes regardless of how much computing power joins or leaves the network. At peak hash rates in 2023–2024, Bitcoin consumed roughly 120–150 TWh of electricity annually — comparable to some mid-sized countries.