Rails 5.2 ships with a new library to support file uploads: Active Storage. In this talk, we will analyze its internal code, learning how it integrates with Active Record and Action Pack to supply amazing features out of the box, from image previews to cloud storage. We will review its class architecture and delve into the implementation of several Active Storage methods, such as has_one_attached and upload. On the way, we will better understand some Ruby patterns frequently used within Rails: meta-programming, macros, auto-loading, initializers, class attributes.