Here Mudassar Ahmed Khan has explained what is Parallel LINQ (PLINQ) and a simple example how to write a PLINQ Query in C# and VB.Net .Net 4.0 and .Net 4.5.
Parallelism can be achieved in two ways
1. Parallel class
2. PLINQ (Parallel LINQ)
Here he has explained how to achieve parallelism using Parallel LINQ (PLINQ).