Modern web applications are made up of many different components. Second only to functionality, the presentation of our application might be considered the most important aspect of our application. Presentation of our user interface and the corresponding user experience is vital to building excellent web applications. In web applications, the presentation and experience is usually defined by Cascading Style Sheets (CSS), and JavaScript files. With raw HTML, we can include any necessary scripts and styles we need to, however often we need to handle our assets in a programmatic way (such as when using modules, components, or widgets). To help manage our assets, we can use a combination of third-party tools and Yii2's built-in asset manager. In this chapter, we'll cover how to use Yii2's asset management tools, as well as cover several third-party tools we can use to simplify management of our asset files.