How do you write a GUI app in a functional programming language that prefers immutability? From Visual Basic on we have been taught how to compose interactive UIs using events and mutable properties. Is there any other way? The answer is, yes, indeed there is. Not only can you build UIs using functional concepts, but I will argue that the architecture of such an app is more modular and more robust than the standard architecture resulting from objects sending messages to each other. This talk is an introduction to the fringe world of functional programming using F# and will have information useful to both beginners and practitioners.