What is bridge?

A service that moves an asset from one blockchain to another, usually by locking it on the source chain and issuing a wrapped version on the destination.

Bridges have been the target of some of the largest hacks in crypto and carry risk beyond the underlying asset.

Nothing actually crosses. The asset stays on the chain it started on, locked in a contract, while a claim on it is issued elsewhere. Understanding that is most of what you need, because it tells you exactly what can go wrong: the claim can survive while the thing it claims does not.

How it works

The common design is lock and mint. You deposit an asset into a contract on the source chain. A set of validators, an oracle network, or a proof system observes that deposit and authorizes a mint of a wrapped token on the destination. Returning burns the wrapped token and unlocks the original.

Who authorizes the mint is the whole security question. A multisig of a handful of signers is the weakest common arrangement, and it is the one that has been compromised most often. Larger validator sets are better; systems that verify the source chain cryptographically are better still.

A canonical bridge is the one operated by a rollup itself, which inherits security from the settlement chain and typically imposes a challenge delay on withdrawals. That delay is a feature, and third-party bridges advertising instant withdrawals are usually lending you funds against a pending claim rather than removing the delay.

Liquidity-network designs work differently: rather than minting, they pay you from a pool already sitting on the destination chain and rebalance later. That removes the mint risk and adds a dependency on pool depth.

Fees combine a bridge charge with the network fee on both chains, so a small transfer can be dominated by the fixed costs.

Example

Illustrative: you bridge 1,000 USDC from Ethereum to a layer 2 network. You pay $4 in Ethereum gas to deposit, a $1 bridge fee, and $0.05 in destination gas. You receive 994.95 USDC-equivalent on the destination, and 1,000 real USDC now sits locked in a contract on Ethereum. If that contract is drained, your destination tokens still exist and are backed by nothing, which is exactly what has happened in several large bridge failures.

Why it matters when you buy

Bridging is often unnecessary. If you are buying an asset that already trades natively on the chain you want, buying it there directly avoids the bridge entirely, and exchanges frequently support withdrawal straight to the destination network. Compare withdrawal network options at the fee comparison and see the guide on sending crypto across chains.

Related terms

• wrapped token — the claim issued on the destination chain
• canonical bridge — the rollup's own, higher-security route
• cross chain messaging — the general problem bridges solve
• atomic swap — a trustless alternative with narrow applicability
• counterparty risk — what a bridge adds to holding an asset
• liquidity — what liquidity-network bridges depend on

Questions

Is a bridge safer than an exchange transfer?

Usually not. Withdrawing from an exchange directly to the destination network avoids the bridge contract entirely, and major exchanges support this for common networks. Compare the fees before assuming the bridge is cheaper.

Why do some withdrawals take a week?

Optimistic rollups have a challenge period during which a withdrawal can be disputed, commonly around seven days. That delay is what makes the security model work.

Are all wrapped tokens the same?

No. Different bridges issue different wrapped versions of the same asset, and they are not interchangeable. Check which version a venue or pool actually accepts.