The programming language primarily used for iOS app development is Swift. Introduced by Apple in 2014, Swift is designed to be easy to read and write, offering a modern syntax and safety features that prevent common programming errors. Its interoperability with Objective-C allows developers to leverage existing codebases while creating new applications. Swift's performance optimizations make it suitable for building high-performance iOS applications, encompassing television apps, games, and innovative software solutions in the Apple ecosystem.