Proof of work (PoW) is a blockchain consensus mechanism that requires significant computing effort from a network of devices. The concept was adapted from digital tokens by Hal Finney in 2004 through the idea of "reusable proof of work" using the 160-bit secure hash algorithm 1 (SHA-1).

Following its introduction in 2009, Bitcoin became the first widely adopted application of Finney's PoW idea (Finney was also the recipient of the first bitcoin transaction). Proof of work is also the mechanic used in many other cryptocurrencies.