Layer-2 solutions are essential for improving the scalability of blockchains. By enabling faster and less costly transactions, they address the limitations of first-layer blockchains like Ethereum. Among the most popular are Optimistic Rollups, which group multiple transactions to reduce congestion, and ZK-Rollups, which use zero-knowledge proofs to validate off-chain transactions. State Channels and Plasma also help to reduce costs and improve the efficiency of dApps. These solutions pave the way for broader adoption of DeFi, NFTs, and real-time applications by making transactions more affordable and faster. Layer-2 is therefore crucial for the future of crypto and blockchain.