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Each L2 (and each chain) has its own state. To use assets across them you need a bridge that moves value between layers.

Bridges let you take ETH on Ethereum and use it on Arbitrum, Optimism, or other networks.

A bridge coordinates two chains so that locking or burning an asset on one side results in receiving it on the other.

The total supply is preserved — assets are not duplicated, just represented on the destination chain.

The most common pattern is lock-and-mint:

• Lock the asset in a contract on the source chain
• Mint a wrapped representation on the destination chain

To move back, the reverse happens — burn-and-release:

• Burn the wrapped asset on the destination chain
• Release the locked original on the source chain

A native (canonical) bridge is operated by the rollup itself and is the most trust-minimized path.

Third-party bridges offer faster or cheaper transfers but add extra trust assumptions in their own contracts and operators.

On rollups, deposits (L1 to L2) are usually fast. Withdrawals (L2 to L1) can be slow.

Optimistic rollup withdrawals wait out the challenge window; ZK rollup withdrawals wait for proof verification.

To avoid long waits, liquidity bridges keep pools of assets on both chains.

You hand assets to a pool on one side and instantly receive from the pool on the other, paying a small fee instead of waiting.

Bridged tokens are often wrapped representations (like USDC.e). Their value depends entirely on the assets locked in the bridge.

If the bridge is hacked and the locked assets are stolen, the wrapped tokens can become worthless.

Bridges do more than move tokens — they pass messages between chains, enabling cross-chain calls and governance.

This general message-passing capability is the basis of advanced interoperability, covered in a later lesson.

The safety of bridged funds depends on the bridge's design. Always ask:

• Who can mint the wrapped tokens?
• How are the locked assets secured?
• Is it canonical or third-party?

Bridges move value across layers using lock-and-mint and burn-and-release, with native bridges being most trust-minimized. Liquidity bridges trade fees for speed.

Next we compare specific L2s to learn how to choose one.

You learned that:

• Bridges move value between layers
• Lock-and-mint and burn-and-release preserve supply
• Native bridges are most trust-minimized
• Liquidity bridges offer speed for a fee
• Bridge trust assumptions determine safety

Next: choosing the right Layer 2.