Ethereum's base layer (Layer 1) prioritizes security and decentralization, which limits how many transactions it can process directly. As usage grew, this led to higher fees and slower confirmation times during periods of network congestion.
Layer 2 solutions address this by processing transactions off the main Ethereum chain while still relying on it for final security and settlement. Rollups are the most widely adopted approach: they bundle, or "roll up," many transactions into a single batch that gets posted back to Ethereum.
Optimistic rollups assume transactions are valid by default and only run a computation to check them if someone disputes a result within a challenge window. This keeps costs low but means withdrawals back to the main chain can take time to finalize.
Zero-knowledge (ZK) rollups instead generate a cryptographic proof that a batch of transactions was processed correctly, which Ethereum can verify almost immediately. This allows faster finality at the cost of more complex proof-generation technology.
Both approaches share the same goal: letting Ethereum scale to far more users and transactions per second while still inheriting the base layer's security guarantees, rather than trading security away for speed.
