In recent years, Functional Programming has stormed software development in a similar way to Object Oriented programming 20 years ago. The promises of stateless coding and immutable data are powerful and seductive to developers of all kinds. Are these promises as good as they sound? Functional Programming is not new, it’s been around for a long time, albeit in different guises, so why is it taking over now? This talk will cover the recent meteoric rise of FP, it will discuss the factors that have come about that have enabled the rapid rise of the new generation of FP styles. Specifically, it will discuss the implications of the FP stateless programming style in a stateful world. Is it really possible to do FP in a stateful world? Or are we creating pseudo statelessness? How do you manage state in FP? Should you even try? It will also look at the philosophy and techniques of FP, the things that it is suited to and the things to which it is not suited. From LISP to Kotlin, FP has gone from early trailblazer, to legacy dinosaur, to the cool kid in town – which narrative should you believe?