MEV

MEV, originally 'miner extractable value' and now usually 'maximal extractable value', is the profit that whoever orders transactions in a block can capture by inserting, reordering, or excluding transactions. Because block producers and specialized searchers can see pending transactions before they are finalized, they can position their own trades around yours to extract value — a structural feature of public blockchains rather than a bug in any one application.

A concrete example: a large swap sits in Ethereum's public mempool, guaranteed to push a token's price up. A searcher's bot spots it and executes a sandwich attack — buying just before the victim's trade and selling just after — pocketing the price move the victim caused. Other MEV forms include arbitrage between exchanges (generally considered benign, since it aligns prices) and liquidations, where bots race to claim liquidation bonuses on lending protocols.

On Ethereum, an entire supply chain has formed around MEV: searchers find opportunities, builders assemble blocks, and validators sell the right to order transactions through systems like MEV-Boost, capturing part of the value as extra revenue. A common misconception is that all MEV is theft — arbitrage and liquidations perform useful market functions, while front-running and sandwiching are extractive. Users can reduce their exposure by setting tight slippage limits and routing transactions through private channels that bypass the public mempool.