A protocol that enables transferring assets between different blockchain networks that can't natively communicate.
A blockchain bridge is a protocol that enables the transfer of assets and data between two or more independent blockchain networks. Since blockchains like Ethereum, Solana, and Avalanche are separate systems with no native ability to communicate, bridges serve as connective infrastructure. The most common mechanism is lock-and-mint: a bridge locks your tokens on the source chain and mints equivalent wrapped tokens on the destination chain. When you bridge back, the wrapped tokens are burned and originals unlocked. Bridges are critical infrastructure for the multi-chain ecosystem but have been the most exploited category in crypto — the Ronin ($625M), Wormhole ($320M), and Nomad ($190M) hacks collectively lost over $1 billion. This is because bridges hold large pools of locked assets and their cross-chain verification logic is complex and difficult to secure. Users should prefer official chain bridges and established protocols with strong security track records.
Blockchain bridges enable asset and data transfer between different blockchains that otherwise cannot communicate — like converting ETH on Ethereum to wrapped ETH on Arbitrum, or moving USDC from Solana to Polygon. Bridges are among the most critical and dangerous infrastructure in crypto: they hold massive pools of locked assets (making them honeypots for hackers) and their security models vary dramatically. Bridge hacks have caused billions in losses — Ronin Bridge ($625M), Wormhole ($325M), Nomad ($190M), and Harmony Horizon ($100M). Bridge designs range from trusted (relying on a multisig of operators), to optimistically verified (assuming transactions are valid unless challenged), to trustless (using cryptographic proofs to verify cross-chain state). The security spectrum matters enormously: trusted bridges are simpler but have single-point-of-failure risk, while trustless bridges using ZK proofs are most secure but technologically complex.
To use a DeFi protocol on Arbitrum, a user bridges ETH from Ethereum mainnet through the official Arbitrum Bridge — the ETH is locked on Ethereum and equivalent ETH appears on Arbitrum within minutes, at a fraction of mainnet gas costs.
Bridges are one of crypto's highest-risk infrastructure components — multiple bridges have been hacked for hundreds of millions. Use only well-established bridges (official L2 bridges, Wormhole, Stargate) and minimize the time assets spend in transit. For large amounts, consider using centralized exchanges as an intermediary — deposit on one chain, withdraw on another.