Bitcoin white paper
The nine-page document in which Satoshi Nakamoto described Bitcoin in 2008: a system of electronic cash between people, with no banks or intermediaries.
On October 31, 2008, a person or group using the pseudonym Satoshi Nakamoto sent the paper Bitcoin: A Peer-to-Peer Electronic Cash System to a cryptography mailing list. In nine pages, it explains how to send online payments directly from one person to another without going through a financial institution.
The problem it solves is double spending: how to stop someone from spending the same money twice without a central authority to check. The answer combines a network of nodes that share one ledger, blocks of transactions chained together, and proof of work, which makes rewriting that ledger very expensive. The network went live in January 2009 and still runs on these ideas.
It is the starting point for understanding Bitcoin: short, technical but clear, and still relevant.
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