---
title: Introduction
framework: cocoa
role: article
path: apple-archive/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Introduction
---

# Introduction

Describes the Objective-C 2.0 runtime support library.

## Organization of This Document

This document has the following chapters:

- [Runtime Versions and Platforms](../Articles/ocrtVersionsPlatforms.html#//apple_ref/doc/uid/TP40008048-CH106-SW1) - [Interacting with the Runtime](../Articles/ocrtInteracting.html#//apple_ref/doc/uid/TP40008048-CH103-SW1) - [Messaging](../Articles/ocrtHowMessagingWorks.html#//apple_ref/doc/uid/TP40008048-CH104-SW1) - [Dynamic Method Resolution](../Articles/ocrtDynamicResolution.html#//apple_ref/doc/uid/TP40008048-CH102-SW1) - [Message Forwarding](../Articles/ocrtForwarding.html#//apple_ref/doc/uid/TP40008048-CH105-SW1) - [Type Encodings](../Articles/ocrtTypeEncodings.html#//apple_ref/doc/uid/TP40008048-CH100-SW1) - [Declared Properties](../Articles/ocrtPropertyIntrospection.html#//apple_ref/doc/uid/TP40008048-CH101-SW1)

## See Also

*[Objective-C Runtime Reference](https://developer.apple.com/documentation/objectivec/objective_c_runtime)* describes the data structures and functions of the Objective-C runtime support library. Your programs can use these interfaces to interact with the Objective-C runtime system. For example, you can add classes or methods, or obtain a list of all class definitions for loaded classes.

*[Programming with Objective-C](../../ProgrammingWithObjectiveC/Introduction/Introduction.html#//apple_ref/doc/uid/TP40011210)* describes the Objective-C language.

*[Objective-C Release Notes](../../../../../releasenotes/Cocoa/RN-ObjectiveC/index.html#//apple_ref/doc/uid/TP40004309)* describes some of the changes in the Objective-C runtime in recent releases of OS X.

[Next](../Articles/ocrtVersionsPlatforms.html)

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