One of the crucial elements of performance is to ship relevant content to your users as soon as possible. But in modern web applications, figuring out what to ship and what to prioritize can be hard. Framework driven applications have the big disadvantage of being pretty heavy for the initial load. We will start from understanding how the browser works, then we will explain what the critical rendering path is and how we can optimize it. Expect a talk full of valuable resources and ideas that one can use to improve the performance of a modern web application, with a case study on a React powered application.