Loopring is an open protocol for building decentralized exchanges. Loopring operates as a public set of smart contracts responsible for trade and settlement, with an off-chain group of actors aggregating and communicating orders. The protocol is free, extensible, and serves as a standardized building block for decentralized applications (dApps) that incorporate exchange functionality. It also offers the ability for orders to be mix-and-matched with other, dissimilar orders, obviating the constraints of two-token trading pairs and improving liquidity. Loopring employs a solution to prevent front-running, and is deployable on any blockchain with smart contract functionality.