Many of the best resources on Cocoa development are installed on your hard drive when you install Apple's Developer Tools. These documents, mirrored online (http://developer.apple.com/techpubs), include but aren't limited to the following:
Updated with every release of Mac OS X, these notes are typically one step ahead of the rest of Apple's documentation. You should read through these every time you update your system so that you can stay on top of the latest changes to the system.
This is the definitive reference for the Objective-C programming language, and is a must-read for all Cocoa developers. HTML and PDF versions of this document can be found on the Cocoa Documentation web site and on your system.
This is a two-volume set, published by Apple through Vervanté, contains the complete reference documentation for the Foundation framework. This is the same material found online at Apple's Cocoa documentation web site, and on your hard drive as part of the developer tools installation.
Like the Foundation Reference for Objective-C, this book is a three-volume set that contains the complete reference documentation for the Application Kit framework.
This overview of Mac OS X is valuable for anyone doing software development with Cocoa. You should read Inside Mac OS X: System Overview to familiarize yourself with the architecture of Mac OS X so you can take advantage of its design. This guide not only describes the features and capabilities of the operating system, it also describes concepts, facilities, and conventions common to the system's Carbon, Cocoa, Java, and BSD application environments.
This book, commonly referred to as "The HIG," describes how to design your application for Mac OS X's user interface (known as Aqua). The HIG provides examples of how to use such Aqua interface elements as windows, controls, dialogs, and icons so that the users of your Cocoa application will be familiar and comfortable with your product the moment they double-click its icon.
This book tells you how to enhance your program to achieve maximum performance and how to use the development tools to analyze and tune your code. Topics include: managing virtual memory; accessing files efficiently; optimizing Carbon applications; building efficient C, C++, and Java code; using the Mac OS X performance measurement and analysis tools; and optimizing the in-memory layout of your program.
Cocoa is built upon the Core Foundation framework. Occasionally, you will need to use functionality at the Core Foundation level that isn't exposed in the Cocoa APIs.
If you prefer print over PDF, you can order printed, bound copies of many selected Apple documents, including the full Cocoa API reference, from Apple's print-on-demand service from Vervanté. For more information, or to order an Apple document, see:
In total, the complete bound Objective-C references for Foundation and Application Kit span 5 volumes and nearly 3,000 pages of material.