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What is a layer 2?
A layer 2 is a separate blockchain that processes transactions off a base chain such as Ethereum, then posts the results back to it. Batching many transactions into one posting spreads the base-chain fee across users, so each transaction usually costs less.
What it means for you
Funds on a layer 2 are not on Ethereum mainnet: to move them back you withdraw through the network's bridge, which on optimistic rollups takes roughly seven days. ethereum.org notes that no layer 2 is as tested as Ethereum mainnet; check which network a wallet is set to before sending.
A common mistake: “Tokens on a layer 2 are on Ethereum.”
In fact: They are balances on a separate chain. Moving them to Ethereum mainnet means withdrawing through the network's bridge, which on an optimistic rollup takes about seven days.
How it works
A layer 2 runs its own chain, processes transactions there and settles them on Ethereum mainnet. Rollups bundle hundreds of transactions into one layer-1 transaction, so the layer-1 fee is shared. Optimistic rollups assume a batch is valid and leave a window to challenge it; zero-knowledge rollups post a validity proof with each batch. Once the data is on layer 1, reverting a rollup transaction requires reverting Ethereum, which is how rollups inherit its security. Sidechains differ: they run their own consensus and do not inherit Ethereum's security.
Sources: ethereum.org: Layer 2, ethereum.org: Optimistic rollups, ethereum.org: Sidechains · checked 4 October 2026
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