This article discusses the idea of using functional programming to enrich object-oriented programming in C#.
This article discusses functional programming in C# through algebra, numbers, Euclidean plane and fractals.
Employing functional programming concepts can improve the quality of your code. Though using functional-programming-inspired features [in C#] is not the same as programming in a pure functional language, like Haskell. Or even a hybrid language but with stronger emphasis on the functional side, like F#.
Ed Charbeneau wrote an excellent guide which explains writing functional programming in C# through an example use case.