iOS jailbreaking is the use of a privilege escalation exploit to remove software restrictions imposed by Apple on devices running iOS and iOS-based operating systems. It is typically done through a series of kernel patches. A jailbroken device typically permits root access within the operating system and provides the right to install software unavailable through the App Store. Different devices and versions are exploited with a variety of tools. Apple views jailbreaking as a violation of the end-user license agreement and strongly cautions device owners not to try to achieve root access through the exploitation of vulnerabilities.

While sometimes compared to rooting an Android device, jailbreaking bypasses several types of Apple prohibitions for the end-user. Since it includes modifying the operating system (enforced by a "locked bootloader"), installing non-officially approved (not available on the App Store) applications via sideloading, and granting the user elevated administration-level privileges (rooting), the concepts of iOS jailbreaking are therefore technically different from Android device rooting.

Expanding the feature set that Apple and its App Store have restricted is one of the motivations for jailbreaking. Apple checks apps for compliance with its iOS Developer Program License Agreement before accepting them for distribution in the App Store. However, the reasons for Apple to ban apps are not limited to safety and security and may be regarded as arbitrary and capricious. In one case, Apple mistakenly banned an app by a Pulitzer-Winning cartoonist because it violated its developer license agreement, which specifically bans apps that "contain content that ridicules public figures." To access banned apps, users rely on jailbreaking to circumvent Apple's censorship of content and features. Jailbreaking permits the downloading of programs not approved by Apple, such as user interface customization and tweaks.

Software programs that are available through APT or Installer.app (legacy) are not required to adhere to App Store guidelines. Most of them are not typical self-contained apps, but instead are extensions and customizations for iOS or other apps (commonly called tweaks). Users can install these programs for purposes including personalization and customization of the interface using tweaks developed by developers and designers, adding desired features such as access to the root file system and fixing annoyances, and making development work on the device easier by providing access to the file system and command-line tools. Many Chinese iOS device owners also jailbreak their phones to install third-party Chinese character input systems because they are easier to use than Apple's.

In some cases, jailbreak features are adopted by Apple and used as inspiration for features that are incorporated into iOS and iPadOS.

Jailbreaking also opens the possibility for using software to unofficially unlock carrier-locked iPhones so they can be used with other carriers. Software-based unlocks have been available since September 2007, with each tool applying to a specific iPhone model and baseband version (or multiple models and versions). This includes the iPhone 4S, iPhone 4, iPhone 3GS, and iPhone 3G models. An example of unlocking an iPhone through a Jailbreak utility would be Redsn0w. Through this software, iPhone users will be able to create a custom IPSW and unlock their device. Moreover, during the unlocking process, there are options to install the iPad baseband to the iPhone.

Cybercriminals may jailbreak an iPhone to install malware or target jailbroken iPhones on which malware can be installed more easily. The Italian cybersecurity company Hacking Team, which used to sell hacking software to law enforcement agencies, advised police to jailbreak iPhones to allow tracking software to be installed on them.

On iOS devices, the installation of consumer software is generally restricted to installation through the App Store. Jailbreaking, therefore, allows the installation of pirated applications. It has been suggested that a major motivation for Apple to prevent jailbreaking is to protect the income of its App Store, including third-party developers and allow the buildup of a sustainable market for third-party software. However, the installation of pirated applications is also possible without jailbreaking, taking advantage of enterprise certificates to facilitate the distribution of modified or pirated releases of popular applications.