MEV (Maximal Extractable Value)

Profit that can be captured by reordering, including, or excluding transactions in a block.

MEV is value that block producers can capture by deciding what transactions to include and in what order. Examples: front-running a large trade (buying just before, selling just after), sandwich attacks on DEX swaps, liquidating positions before others can, capturing arbitrage between venues. MEV is extracted by searchers (who find opportunities) and builders/validators (who include the relevant transactions).

MEV is not theoretical — it accounts for hundreds of millions of dollars per year on Ethereum alone. Mitigations include private mempools, MEV-share auctions, and ordering protocols that minimize discretion. Some MEV is welcome (arbitrage that improves price efficiency); much of it is direct value extraction from users.