Rollups are Layer 2 scaling solutions for Ethereum, enhancing speed and reducing costs. There are two main types: Optimistic Rollups and Zero-Knowledge (ZK) Rollups. Optimistic Rollups, implemented by projects like Optimism ($OP) and Arbitrum ($ARB), use fraud proofs to allow challenges to transaction validity, focusing on increasing Ethereum's transaction throughput. Zero-Knowledge Rollups (zk-Rollups), used by zkSync, StarkWare, and Hermes Network, utilize zero-knowledge proofs to enhance scalability and privacy. Both methods bundle multiple transactions into a single proof, verified on the main chain. Optimistic Rollups are generally faster but less secure, while ZK Rollups offer more robust security but can be more complex.