This document provides an introduction to distributed ledgers and blockchain. It explains that a distributed ledger is a digital database containing records that can be seen by all participants in a network. When any change is made to a record, it is automatically updated for all participants so everyone sees the same common view. The document uses a simple example of transactions between banks and customers to illustrate how a distributed ledger provides a single shared view of the truth, as opposed to separate databases that need reconciliation. It also introduces key concepts such as how distributed ledgers bring efficiencies by combining transactions with their recording in a single system.