How it works is complicated. Why it matters is simple. Ethereum provides a guarantee. It guarantees code must run as written. Code, at its lowest level, is a language only machines can understand. Programmers read and write in a translated version of this machine language. But intelligent tools now make it easy to flow back and forth between the language you speak and that previously incomprehensible language known as code. The internet doesn't have laws and can't give people rights. But when code is combined with the guarantees that Ethereum has promised, and vigilantly upheld, for over a decade, a new layer of the internet is formed. A place where money, art, and artifacts can be made incorruptible. Where any kind of rule can be written, made clear, solid, and certain, then applied equally to all. But it's not free. A network of machines must be incentivized to run and keep running. The ecosystem must plan for and defend against new technologies, war, and tyranny. Ethereum must prove its value again and again. It must evolve as the world does. Therefore, what matters most is a broad understanding. As this global experiment in coordination, this thing owned by everyone, is passed on from one generation to the next, there must be some semblance of an enduring soul reflecting at least some part of what its original believers intended the thing to stand for. This book is an effort to add to that collective soul, to help fortify the will and character of this experiment as it marches indefinitely toward an uncertain future.