C#: Covariance and Contravariance

Intro

Every time I google for covariance I end up reading Eric Lippert's blog. He has awesome seria of articles about covariance and contravariance. It was written in 2007, but still useful when you don't know how to explain the variance to somebody who doesn't know how it works for delegates or generic types.

Summary

His blog is quite good, any developer can find something useful there.