Layer 1 (L1) blockchains are the base protocols that secure, validate, and finalize all transactions in a decentralized network. Acting as the operating system for Web3, they provide the core infrastructure for smart contracts, decentralized applications (dApps), and token ecosystems. Examples include Bitcoin, focused on security and decentralization through Proof-of-Work, and Ethereum, which pioneered programmable smart contracts with Proof-of-Stake. Technically, an L1 blockchain manages its own consensus mechanism, transaction finality, and native coin (e.g., BTC, ETH, SOL). It handles the block structure, cryptographic hashing, and Merkle tree verification that ensure immutability and security. While some prioritize decentralization and security, others like Solana and Avalanche optimize for scalability with high TPS and low fees, addressing the blockchain trilemma with innovative consensus models like Proof-of-History or Snowman. As the settlement layer, all Layer 2 scaling solutions and dApps ultimately anchor their data back to an L1 for trust and finality. This makes Layer 1 the bedrock of blockchain ecosystems, driving demand for its native coin as the fuel for transaction fees, staking, and governance.