To many people, System.Collections.Generic.... is just a useful collection. In this post, I'll be looking inside that collection and see how it really works. Dictionary is based on a hashtable; for the rest of this post, I'll assume you know roughly how a hashtable works. The Wikipedia article, as the source of all knowledge algorithmical, provides a good overview. It will also help if you've got the class open in Reflector so you can see what's going on yourself. The basics ......