A Functional Programming developer designs and writes computer programs using the principles of functional programming. They create software applications using pure functions, avoiding shared state, mutable data, and side-effects. They aim to make the software more predictable and easier to test and debug. They use languages like Haskell, Erlang, or Scala. Their tasks include writing clean and efficient code, debugging, testing, maintaining codebases, and sometimes collaborating with other developers. They focus on what the software should accomplish, not how to control its execution. They often work in fields like data science, machine learning, big data, and complex system development.