Layer 1 (L1) refers to the base blockchain network — the foundational layer that processes and finalizes transactions on its own. Examples include Bitcoin, Ethereum, Solana, Avalanche, and BNB Chain.
Function
Layer 1 blockchains establish the consensus mechanism, define the rules for transaction validation, maintain the distributed ledger, and provide the security guarantees that all other layers build upon.
The Blockchain Trilemma
Layer 1 chains face the "blockchain trilemma" — the challenge of simultaneously achieving decentralization, security, and scalability. Different L1s make different tradeoffs: Bitcoin prioritizes security and decentralization, Solana prioritizes speed and scalability.
Layer 1 vs Layer 2
While Layer 1 is the base chain, Layer 2 solutions are built on top to improve scalability. L2s process transactions off the main chain and periodically settle them back on L1, achieving higher throughput and lower fees while inheriting L1's security.