Bootstrap is a free CSS and JavaScript framework that allows developers to rapidly build responsive web interfaces. The framework was first conceived by Mark Otto and Jacob Thornton while working at Twitter in 2010. Since its release as an open source project in August of 2011, Bootstrap has become a household name among frontend web developers. The framework’s ease-of-use along with its cross-browser compatibility, support for mobile user interfaces, and responsive web design capabilities, make it an essential building block for any modern web application. Totaling over 600 contributors, and more than 34,000 GitHub forks, Bootstrap has become the world’s most popular responsive web development framework. However, despite its popularity, there are relatively few advanced resources on the fourth, and latest, version of Bootstrap. As such, the motivation behind this book is to provide a comprehensive, step-by-step guide for developers that wish to build a complete, production-ready, website using Bootstrap 4. Once you turn the final pages of this book, you should be mastering the framework’s ins and outs, and building highly customizable and optimized web interfaces. You will know how to both extend the framework, integrate it with third-party components and frameworks, as well as optimize and automate your Bootstrapped builds.