This is an open access title available under the terms of a CC BY-NC-ND 4.0 International licence. It is free to read on the Oxford Academic platform and offered as a free PDF download from OUP and selected open access locations. A web browser is a pretty unusual piece of software, with unique challenges, interesting algorithms, and clever optimizations. Building a browser is both easy and incredibly hard, both intentional and accidental, and everywhere you look, you see the evolution and history of the web wrapped up in one codebase. It's both fun, and endlessly interesting. Software always runs on some kind of operating system or platform, and a working or budding software engineer always benefits from more deeply understanding that platform. Web browsers are the most common and widely-used platform there is, and this book is the essential description of how they work and how that impacts web developers and other software engineers whose work touches the web. Readers of Web Browser Engineering will be taken through the journey of building their own web browser, including capabilities for rich visual design, multithreaded architecture, JavaScript APIs, and comprehensive security policies. This interactive and engaging source of information will be a unique tool for any software engineer, computer science student, web developer, or simply anyone with an interest in web browsers, and how they work.