When should I use a struct rather than a class in C#?

Question

When should you use struct and not class in C#? My conceptual model is that structs are used in times when the item is merely a collection of value types. A way to

Answer 1

Use a struct when you want value semantics as opposed to reference semantics.

Edit

Not sure why folks are downvoting this but this is a valid point, and was made before the op clarified his question, and it is the most fundamental basic reason for a struct.

If you need reference semantics you need a class not a struct.