Today's blockchain ecosystem has dozens of chains: Ethereum, Polygon, Arbitrum, Optimism, Base, zkSync, and more. Each has different speed, cost, and security trade-offs. Cross-chain refers to moving assets or data between these different blockchains.
Lower fees: Ethereum mainnet gas can cost $10-50 per transaction. Layer 2s (Arbitrum, Optimism) cost cents. Speed: Some chains confirm in seconds vs. Ethereum's ~12 seconds. Access: Some DeFi opportunities only exist on specific chains.
Bridges lock tokens on one chain and mint wrapped versions on another (e.g., WETH on Polygon). Native cross-chain protocols (LayerZero, Wormhole, Axelar) pass messages and liquidity across chains without traditional wrapping.
Why would you move assets from Ethereum to Arbitrum?