Over the last couple of years functional programming languages like Scala, Clojure, or Elixir have gained popularity and acceptance. The first half of the talk will introduce you to the main concepts of functional programming, like higher-order functions, immutable data structures, lazy evaluation, and tail recursion. In the second half we will put those concepts into practice as we step-by-step develop a full web application in Clojure in a test-driven way. This talk is for you, if you agree with Alan Perlis that "a language that doesn’t affect the way you think about programming, is not worth knowing.