Use the Foundation framework for the "nuts and bolts" classes for Objective-C programming. This framework provides essential Objective-C classes, most importantly the root class, NSObject, which defines basic object behavior. It includes classes for objects representing basic data types, collections, and operating-system services. Foundation also introduces several design patterns and mechanisms that contribute to the robustness and efficiency of Objective-C programs. Along with UIKit, the Foundation framework provides the basic tools and infrastructure you need to implement graphical, event-driven iPhone applications.