Layer 2 (L2) solutions are protocols built on top of a base blockchain (Layer 1) to increase transaction throughput and reduce fees. They inherit the security of the underlying L1 while moving computation off-chain.
Rollups are the most prominent L2 approach. Optimistic rollups assume transactions are valid by default and use a fraud-proof window (typically 7 days) during which challenges can be submitted. ZK-rollups use zero-knowledge proofs to mathematically validate batches of transactions, enabling faster withdrawals.
Major L2 networks like Arbitrum, Optimism, zkSync, and Starknet have attracted billions in total value locked (TVL). Ethereum L2s process thousands of transactions per second at a fraction of mainnet costs, making DeFi and NFT applications accessible to a broader user base.