> ## Documentation Index > Fetch the complete documentation index at: https://docs.theblockchainlibrary.com/llms.txt > Use this file to discover all available pages before exploring further. # Blockchain basics > Understand what a blockchain is, how transactions are recorded, and why distributed consensus matters. ## What is a blockchain? A blockchain is a shared data system in which network participants maintain and validate an ordered history of state changes. Depending on the network, those changes can represent asset transfers, smart-contract execution, governance actions, or other records. ## Core building blocks * **Transactions** describe requested state changes. * **Blocks** group ordered transactions or state transitions. * **Nodes** maintain, validate, and relay network data. * **Consensus** determines how the network agrees on valid state. * **Cryptography** supports signatures, integrity, and ownership proofs. ## Why it matters Blockchain systems can reduce dependence on a single database operator when the application benefits from shared verification, programmable assets, transparent rules, or decentralized control. Not every application needs a blockchain. The trade-offs include complexity, public-state exposure, governance constraints, and operational overhead.