Mastering Bitcoin is the book developers point newcomers-to-the-code toward, and for good reason. It explains Bitcoin from keys and addresses through transactions, scripts, the mempool, mining, and consensus, with enough precision that you come away understanding how the machine actually runs rather than just what it is for. O'Reilly and reviewers consistently describe it as the best technical reference on Bitcoin available, and that reputation is deserved.
The 3rd edition matters because Bitcoin changed a lot after the earlier versions. This edition was written by David A. Harding, building on Andreas Antonopoulos's first two editions, with a stated focus on modernizing the 2017 second edition and the leftover 2014 first-edition material. That refresh brings the text closer to modern Bitcoin, including SegWit and Taproot-era concepts, which is exactly where the older editions had started to show their age.
A genuinely important buying note: you do not have to buy it. The complete text of the 3rd edition is published free on GitHub under a Creative Commons license (initially non-commercial/no-derivatives, later moving to a more permissive share-alike license), and you can read every chapter in the browser. The O'Reilly paperback and ebook are for people who prefer a bound copy or want to support the authors. For a Bitcoin shop that's worth stating plainly rather than hiding.
The honest limitation is audience. The book itself says the first two chapters are for everyone and the rest is aimed at developers, engineers, and systems architects, and that is accurate. If you can't read a bit of code or aren't comfortable at a command line, large stretches will wash over you. This is not a knock on the book; it is simply not trying to be a gentle primer, and pretending otherwise sets buyers up for frustration.
Scope is also narrow by design. Mastering Bitcoin explains the technology and almost nothing else. There is no meaningful coverage of price, investing, custody strategy for ordinary users, or the monetary-economics debates that books like Broken Money and The Bitcoin Standard center on. Pair it accordingly.
The other structural caveat is freshness. Bitcoin's tooling and best practices move quickly, so any static print edition drifts over time; the living GitHub repository is the version that stays current. Bottom line: for the right reader this is a five-star, career-useful reference, and the free online availability makes it an easy recommendation. Just make sure the buyer is actually the technical reader this book is written for.