This document provides an overview of iOS, including its history, development tools, programming languages, and software layers. It discusses the Core OS layer, Core Services layer, Media layer, and Cocoa Touch layer that make up iOS. It also lists iOS devices and versions that have been released. Finally, it outlines some new features introduced in iOS 8 like QuickType keyboard, support for third-party keyboards, recent contacts in app switcher, HealthKit, and improved Spotlight search capabilities.