When discussing major cryptocurrencies like Ethereum, a recurring challenge is the "Scalability Trilemma": the difficulty of achieving Decentralization, Security, and Scalability all at once. Base layers (Layer 1) often prioritize the first two, leading to slow transactions and high gas fees during peak usage.

​Enter Layer 2 (L2) Scaling Solutions. These are protocols built on top of the Layer 1 blockchain to handle transactions off-chain, significantly increasing throughput while inheriting the underlying security.

​The two most prominent L2 technologies are:

1. ​Rollups (e.g., Arbitrum, Optimism): These execute transactions off-chain, then "roll up" hundreds of them into a single proof that is posted back to the Layer 1 chain. They are further divided into Optimistic Rollups and ZK-Rollups (Zero-Knowledge).
2. ​Sidechains (e.g., Polygon): These are independent, compatible blockchains with their own consensus mechanisms, connected to the main chain via a two-way bridge.

​L2 solutions are not just upgrades; they are essential infrastructure for mass adoption. They make decentralized applications (dApps) fast and affordable, paving the way for Web3 and DeFi to reach billions of users.