A working or budding software engineer always benefits from deeply understanding the platform their code runs on, and web browsers are the most common and widely-used platform there is. 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 join the authors in building their own web browser, including rich visual effects, multithreaded architecture, JavaScript APIs, and comprehensive security policies. Web browser engines are filled 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. This interactive and engaging book will be a unique source for any software engineer, computer scientist, web developer, or simply anyone with an interest in web browsers and how they work. 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.