Cocoa consists of many frameworks that allow you to conveniently access iPhone OS and Mac OS X features and incorporate them into your apps. The Cocoa frameworks help you create apps which adhere to the Mac’s unique look and feel. In the Cocoa Resource Center, you'll find links to:

• The blog, "Basics for new Mac and iPhone Programmers," by Derek Underwood.
• The Cocoa & Cocoa Touch page on the Apple Developer Connection.
• CocoaDev—a resource site for Mac OS X developers.
• Apple’s Cocoa Guides. Topics include accessibility, audio, data management, design guidelines, games, graphics and imaging, networking, performance, security, tools and more.
• The AppKiDo free reference tool that helps programmers locate what they need in the Cocoa documentation.
• An online Cocoa Programming course from Stanford University, available for download from iTunes U.
• The sample chapter, "Cocoa: What It Is," from Cocoa Programming for Mac OS X, 3/e, by Aaron Hillegass.
• The article, "Cocoa for Scientists: Developing for iPhone," by Drew McCormack.
• The article, "Cocoa Style for Objective-C: Part I," by Scott Stevenson.
• The "Late Night Cocoa," podcast series for Cocoa developers.
• Apple Developer Network podcasts.
• Xcode, Cocoa,Objective-C video tutorials for iPhone developers.
• The video, "Building A Cocoa Calculator App Using Xcode 3."
• The "Cocoa Game Programming Workshop," by David Hill.
• "Cocoa Touch Tutorial: iPhone Application Example," by Matt Long.
• "Cocoa Tutorial: Fixing Memory Leaks with Instruments," by Matt Long.
• The Cocoa Tutorial for Beginners.
• Cocoa blogs, books, forums, source code, tools and more...