Companies adopt Lean because it is a proven path to improving delivery times, reducing cost, and improving quality. A company that writes software cannot truly embrace Lean without also embracing functional programming. Why? Lean is about building quality into the process. Lean is a systemic method for reducing waste, overburden, and inconsistency. With OO, many forms of waste, overburden, and inconsistency are unavoidable. A defect early in the process always results in a defect in the product later in the process, and OO itself is a defective process. In this session we will go from the origins of both Lean and FP and see how specific FP concepts (examples in F#, Elixir) map onto Lean principles. We will also discuss why some companies fail at Lean and FP.