This is a tutorial on using Functional Programming (FP) techniques for constructing LINQ queries. It is certainly possible to write simple LINQ queries without using these techniques, but as soon as you start writing more complicated queries, you need to understand these techniques.

1. Introduction to the FP Tutorial

Introduces functional programming, mentions some of the core ideas, and the main hurdle (lazy evaluation) that users of LINQ will have to jump.

(Eric White)