We are working on putting together a session for MSDN Events on LINQ and how it changes the way that developers work with data in their applications. The basic question of what is LINQ is fairly straightforward, in that it is the name given to a collection of new language features that are part of .NET 3.5. While the next framework (3.5) does add a number of components for LINQ, it also utilizes a number of language features that were added in previous versions including 2.0 and 3.0.
Daniel Moth is a former MVP who has been blogging recently (http://www.danielmoth.com) on LINQ and even posted a video on Channel9 which does a great job of describing how LINQ evolves from existing language features. I summarize some of the points on how he does it with some screen shots, etc., but to get the most from it, click on the link & watch it for yourself.