The primary programming language used for developing iOS applications is Swift. Launched by Apple in 2014, Swift is designed for safety, performance, and expressiveness, making it easier for developers to create robust applications. Its modern syntax and rich features enable developers to write clean and maintainable code while benefiting from performance optimizations that enhance app speed and responsiveness. Swift supports both object-oriented and functional programming paradigms, catering to diverse development needs. Additionally, it boasts an active community and extensive resources, further promoting its adoption among iOS developers.