This document discusses the Model-View-Controller (MVC) design pattern and view controllers in iOS. It explains that MVC separates an app into three components: the model (data), the view (user interface), and the controller (logic). The controller manages the model and view, and allows them to communicate indirectly. View controllers are the main interface between views and models, and their lifecycle methods like viewDidLoad are described. Common iOS view controllers like UITabBarController and UINavigationController are also mentioned.