iPhone OS 1 is the first release of what is now iOS, the mobile operating system Apple shipped on the original iPhone on June 29, 2007. At launch it had no version branding at all: Steve Jobs introduced the phone as running "OS X," and Apple's early materials avoided naming the system entirely. The retroactive name "iPhone OS 1" settled in once iPhone OS 2 formalized the versioning in 2008.

Whatever its name, the software was the iPhone's real revolution. It brought a desktop-class WebKit browser, capacitive multi-touch with inertial scrolling and pinch-to-zoom, visual voicemail, and a fixed grid of core apps — and it did so with no native third-party apps, no App Store, no copy and paste, no MMS, and no home-screen customization. Jobs's answer to developers — write web apps for Safari — held for exactly one year before the App Store reversed it.

The launch system shipped sixteen apps — Phone, Mail, Safari, iPod, Messages (SMS only), Calendar, Photos, Camera, YouTube, Stocks, Maps (Google-backed), Weather, Notes, Clock, Calculator, and Settings — plus multi-touch text handling with the magnifying-glass loupe and predictive keyboard. Its interaction fundamentals (tap, swipe, pinch, momentum scrolling with rubber-band edges) were the product's patent-guarded crown jewels, and its animations ran at a fluidity no 2007 competitor approached.

Point updates added the iTunes Wi-Fi Music Store (1.1.1), and — in the January 2008 "1.1.3" update, a $19.99 paid upgrade for iPod touch owners — home-screen rearrangement, web clips, and multi-recipient SMS.

The original iPhone and the first-generation iPod touch. Both were later eligible for iPhone OS 2 and iPhone OS 3 (the iPod touch via paid upgrades).

iPhone OS 1 is the ancestor of every modern smartphone interface: its multi-touch grammar and app-grid home screen became the industry's defaults within two years. Its restrictions defined the platform's early identity fights — the jailbreak community formed around them almost immediately — and their reversal, the App Store in iPhone OS 2, created the app economy. The system's direct descendants run today as iOS 26 and its sibling platforms.