The programming language predominantly used for developing iOS applications is Swift. Introduced by Apple in 2014, Swift is designed to be safe, fast, and expressive, making it suitable for building applications on iOS, macOS, watchOS, and tvOS platforms. It features modern programming constructs and is optimized for performance, allowing developers to write cleaner and more maintainable code. Swift has largely supplanted Objective-C as the preferred language for iOS development, providing a more streamlined experience and enhancing efficiency in the app development lifecycle.