The Objective-C programming language includes a preprocessor that is used to translate source files prior to compilation. Some of the translation is performed automatically, and a portion is performed based on the preprocessor language elements that you include in your source files. If you look at publicly available Objective-C source code, such as Apple’s Objective-C source code for example, you’ll most likely observe liberal use of the preprocessor language. So you may be wondering, what are the features of the preprocessor and how do you best use this language in your programs? Those are the subjects of this chapter, so let’s get started!