Cocoa is Apple's native object-oriented application programming interface (API) for its desktop operating system macOS.

Cocoa consists of the Foundation Kit, Application Kit, and Core Data frameworks, as included by the Cocoa.h header file, and the libraries and frameworks included by those, such as the C standard library and the Objective-C runtime.

Cocoa applications are typically developed using the development tools provided by Apple, specifically Xcode (formerly Project Builder) and Interface Builder (now part of Xcode), using the programming languages Objective-C or Swift. However, the Cocoa programming environment can be accessed using other tools. It is also possible to write Objective-C Cocoa programs in a simple text editor and build it manually with GNU Compiler Collection (GCC) or Clang from the command line or from a makefile.

For end users, Cocoa applications are those written using the Cocoa programming environment. Such applications usually have a familiar look and feel, since the Cocoa programming environment provides a lot of common UI elements (such as buttons, scroll bars, etc.), and automates many aspects of an application to comply with Apple's human interface guidelines.

For iOS, iPadOS, tvOS, and watchOS, APIs similar to Application Kit, named UIKit and WatchKit, are available; they include gesture recognition, animation, and a different set of graphical control elements that are designed to accommodate the specific platforms they target. Foundation Kit and Core Data are also available in those operating systems. It is used in applications for Apple devices such as the iPhone, the iPod Touch, the iPad, the Apple TV, and the Apple Watch.

Cocoa continues the lineage of several software frameworks (mainly the App Kit and Foundation Kit) from the NeXTSTEP and OpenStep programming environments developed by NeXT in the 1980s and 1990s. Apple acquired NeXT in December 1996, and subsequently went to work on the Rhapsody operating system that was to be the direct successor of OPENSTEP. It was to have had an emulation base for classic Mac OS applications, named Blue Box. The OpenStep base of libraries and binary support was termed Yellow Box. Rhapsody evolved into Mac OS X, and the Yellow Box became Cocoa. Thus, Cocoa classes begin with the letters NS, such as NSString or NSArray. These stand for the original proprietary term for the OpenStep framework, NeXTSTEP.

Much of the work that went into developing OpenStep was applied to developing Mac OS X, Cocoa being the most visible part. However, differences exist. For example, NeXTSTEP and OpenStep used Display PostScript for on-screen display of text and graphics, while Cocoa depends on Apple's Quartz (which uses the Portable Document Format (PDF) imaging model, but not its underlying technology). Cocoa also has a level of World Wide Web support, including the NSURL and WebKit HTML classes, and others, while OpenStep had only rudimentary support for managed network connections via NSFileHandle classes and Berkeley sockets.

The API toolbox was originally called “Yellow Box” and was renamed to Cocoa - a name that had been already trademarked by Apple. Apple's Cocoa trademark had originated as the name of a multimedia project design application for children. The name was intended to evoke "Java for kids", as it ran embedded in web pages. The original "Cocoa" program was discontinued following the return of Steve Jobs to Apple. At the time, Java was a big focus area for the company, so “Cocoa” was used as the new name for “Yellow Box” because, in addition to the native Objective-C usage, it could also be accessed from Java via a bridging layer. Even though Apple discontinued support for the Cocoa Java bridge, the name continued and was even used for the Cocoa Touch API.