Glossary
Bridge (cross-chain bridge)
A crypto bridge (cross-chain bridge) is a protocol that moves tokens or data from one blockchain to another, usually by locking the assets on the source chain and issuing an equivalent token on the destination chain, or by using liquidity on both sides.
Also called Cross-chain bridge, Blockchain bridge, Token bridge, Interoperability protocol
See also
A crypto bridge, or cross-chain bridge, connects two blockchains that cannot talk to each other natively. Bitcoin, Ethereum, Solana or a rollup each keep their own ledger, so a token cannot simply “travel” from one to another. A bridge creates the link: you send assets on one chain and receive their equivalent on the other.
How a bridge works
There are three common designs:
- Lock and mint: you deposit tokens in a contract on chain A; the bridge mints the same amount of “wrapped” tokens on chain B. To go back, the wrapped tokens are burned and the originals are released.
- Burn and mint: the token issuer destroys tokens on one chain and creates them on another, so no wrapped version is needed.
- Liquidity networks: the bridge holds pools of the same asset on both chains and pays you from the destination pool, then rebalances.
Someone has to confirm that the deposit really happened. Depending on the bridge, that is a small group of validators, a larger decentralized network, or cryptographic proofs verified on-chain. Bridges between Ethereum and a layer-2 are often built into the rollup itself and use its security model.
A simple example
You hold 1,000 USDC on Ethereum and want to use an app on another chain. You approve the bridge, deposit 1,000 USDC and pay a fee of, say, $3. A few minutes later you receive 997 bridged USDC on the destination chain. Your original USDC sits in the bridge contract. If that contract is drained, your bridged tokens may lose their backing.
Why bridges matter
Users, liquidity and applications are spread across many networks. Bridges let capital move to where it is needed and make a multi-chain ecosystem usable.
Risks and limits
Bridges concentrate large amounts of locked assets, which makes them prime targets. In March 2022, attackers gained control of five of the nine validator keys of the Ronin bridge, used by the game Axie Infinity, and withdrew about 173,600 ETH and 25.5 million USDC, worth roughly $625 million at the time. In April 2022, US authorities linked the theft to North Korea’s Lazarus Group.
- Smart contract bugs and compromised keys can wipe out the backing of wrapped tokens.
- A bridge run by a few validators is only as safe as those operators.
- Fake bridge sites are a common phishing trap; see how to avoid crypto scams.
- Sending to an unsupported chain or address can mean a permanent loss.