SwiftUI and UIKit represent different approaches to iOS app development. SwiftUI uses declarative syntax where you describe what the UI should do. UIKit uses imperative code where you control UI programmatically. SwiftUI is Apple's future direction with new features landing first. UIKit has 14+ years of maturity and extensive third-party library support. SwiftUI supports fewer iOS versions (iOS 15+ recommended). UIKit supports iOS 13 and earlier versions. SwiftUI's preview system UI iteration. UIKit requires building and running for visual feedback. SwiftUI has built-in Dark Mode and Dynamic Type support. UIKit requires manual adaptation for these features. SwiftUI creates consistent apps across Apple platforms. UIKit is specific to iOS and tvOS. SwiftUI's NavigationStack and NavigationSplitView simplify navigation. UIKit's NavigationController provides mature navigation patterns. SwiftUI state management with @State, @Binding, and @ObservableObject is simpler. UIKit's delegate pattern can be verbose. Choose SwiftUI for new projects targeting recent iOS versions. Choose UIKit for complex custom UI or backward compatibility. Both frameworks can coexist in the same project.