The programming language primarily associated with iOS app development is Swift. Introduced by Apple in 2014, Swift is designed to be powerful yet easy to use, emphasizing performance and safety. It replaces Objective-C as the preferred language for iOS development, allowing developers to create apps that are more efficient and less prone to errors. Swift's modern syntax and features, such as closures, generics, and type inference, facilitate rapid development and enhance code maintainability. This language is fundamental for building applications on the Apple ecosystem, including iOS, macOS, and watchOS.