The blockchain is the underlying technology behind cryptocurrencies like Bitcoin, consisting of several 'blocks' of data 'chained' together into a single system. It acts as a decentralised public ledger, tracking every transaction that takes place on the network. Multiple miners work together to reach consensus on whether to add individual Bitcoin transactions to the blockchain, since no person or group has central authority over it. This takes place through the Proof of Work (PoW) consensus mechanism. Each transaction on the blockchain includes inputs and outputs. Outputs include instructions for sending Bitcoin and the value they’ll be worth when claimed. Inputs are references to outputs from previous transactions, and most transactions contain two or more inputs. Bitcoin was the first blockchain, but every crypto token has one. Altcoins like Ethereum work slightly differently, but the fundamentals are similar.