A common programming language used for developing iOS applications is Swift. Introduced by Apple, Swift is designed for safety, performance, and expressiveness, making it accessible for both new and experienced developers. It integrates seamlessly with existing Objective-C code, allowing for smooth transitions in legacy applications while also supporting modern coding practices. Swift's features, like type safety and syntax brevity, enhance development efficiency and maintainability. As a result, Swift remains a popular choice for building native iOS and macOS applications.