Proof of Work
A consensus mechanism requiring miners to solve computationally expensive puzzles to propose new blocks.
Proof of Work (PoW) is the original blockchain consensus mechanism, pioneered by Bitcoin. Miners compete to find a nonce value that, when hashed with the block data, produces a hash below a target threshold. This process requires significant energy and acts as a Sybil-resistance mechanism — it costs real resources to cheat.
The miner who finds a valid hash first broadcasts the block to the network, which verifies it instantly (verification is cheap even though finding the hash is expensive). The winner receives the block reward plus transaction fees.
PoW's main criticism is its energy consumption. Bitcoin's network consumes electricity comparable to some mid-sized countries. Ethereum migrated away from PoW to Proof of Stake in 2022's Merge.