structural:scholar_edition, quality:correction, information:filtering, quality:corruption
App Store and third-party apps

At WWDC 2007 on June 11, 2007, Apple announced that the iPhone would support third-party Ajax web applications that share the look and feel of the iPhone interface. On October 17, 2007, Steve Jobs, in an open letter posted to Apple's "Hot News" weblog, announced that a software development kit (SDK) would be made available to third-party developers in February 2008. The iPhone SDK was officially announced and released on March 6, 2008. The App Store was launched with the release of iPhone OS 2.0, on July 11, 2008.

Apple requires all third-party apps to be downloaded from the App Store, with exceptions for ad-hoc apps used within enterprises. Developers must pay a yearly $99 fee as part of Apple's Developer Program; if their membership expires, their apps are removed from the App Store, though existing users retain the ability to redownload the app. Developers can release free apps, or paid apps for which Apple takes a 30% cut of proceeds. Developers earning less than $1 million in annual sales qualify for the App Store Small Business Program, with Apple only taking a 15% fee.

Though iOS has far lower market share than Android, its app ecosystem has been described as superior, with higher-quality apps, and more iOS-exclusive releases. Android's version fragmentation, less uniform hardware, and lower app revenues have been cited as key factors.

All apps must pass Apple's app review process before being distributed in the App Store. Apple may also stop distributing apps it deems inappropriate. For example, in 2009, Apple rejected the Newspapers app due to The Sun's "obscene" topless Page 3 girls. In 2018, Apple removed Tumblr from the App Store, citing illegal content, causing Tumblr to ban all adult content from their platform. The App Store's review process has been criticized by developers as "frustrating", " anti-competitive ", and "asinine".

Users can also install native apps outside of the App Store through jailbreaking, or through exploits, such as TrollStore. Jailbreaking may cause security issues, and is not supported by Apple.

As of October 2013, Apple has passed 60 billion app downloads. As of September 2016, there have been over 140 billion app downloads from the App Store. As of January 2017, the App Store has over 2.2 million apps for the iPhone.