A Flutter package is a unit of code that is factored out to be reusable and shareable. A Flutter plugin is a special type of package and aims to make native libraries available to your dart code. Most likely your latest Flutter app depends on a number of third-party packages, many of them plugins. Understanding how these are built will help you evaluate available components, extend them to suit your needs, and even write your own plugin from scratch. In this talk, I will discuss the federated architecture of modern Flutter packages, including the special provisions needed for plugins to support a growing number of host platforms. I will then show a concrete example of a plugin package that makes native authentication libraries on iOS and Android available to a flutter widget.