<p>Proof of work (PoW) is a consensus mechanism used in many blockchain networks, requiring participants—called miners—to solve computational puzzles to validate transactions and add new blocks to the chain. By demanding significant processing power, PoW makes it costly to attack the network while allowing honest participants to earn rewards for securing the system.</p>

<h2>How It Works</h2>
<p>In PoW, miners assemble a block of pending transactions and repeatedly hash the block header combined with a variable called a nonce. The goal is to produce a hash output that is lower than a network‑defined target difficulty. Because hash functions are unpredictable, miners must try many nonce values—often billions—before finding a valid solution. The first miner to discover such a hash broadcasts the block to the network. Other nodes verify the proof by performing a single hash check; if the hash meets the difficulty rule, the block is accepted and appended to the blockchain. The successful miner receives a block subsidy (newly created coins) plus any transaction fees included in the block. To keep block times stable, the difficulty adjusts automatically after a set number of blocks, increasing when blocks are found too quickly and decreasing when they are found too slowly.</p>

<h2>Why It Matters</h2>
<p>PoW secures the blockchain by making any attempt to rewrite history prohibitively expensive. An attacker who wants to alter a confirmed block must redo the work for that block and all subsequent blocks, which would require more than 50 % of the total network hash power—a feat that is economically impractical for major cryptocurrencies like Bitcoin. This high cost deters double‑spending and other malicious actions, fostering trust without a central authority. For example, Bitcoin’s PoW has maintained continuous operation and resisted successful attacks since its 2009 launch, enabling a decentralized monetary system that operates globally. The mechanism also incentivizes resource investment in hardware and electricity, aligning participants’ economic interests with network integrity.</p>

<p><strong>Related terms:</strong> proof‑of‑stake, <a href="/NewSite/encyclopedia/mining/" class="ency-link">mining</a></p>