The programming language used exclusively for iOS app development is Swift. Introduced by Apple in 2014, Swift was designed to be fast, safe, and easy to use, allowing developers to create robust applications for iOS, macOS, watchOS, and tvOS. The language features modern syntax and performance improvements over its predecessor, Objective-C. Swift's emphasis on safety helps minimize common programming errors, making it an attractive choice for developers aiming to create high-quality applications. Swift has quickly gained popularity within the Apple developer community and beyond.