There has been a lot of coverage of the housing bubble and of the sloppiness in the mortgage industry that allowed the market to overheat based on loans to people who couldn't pay them back.

But for a quick, interesting, easy to understand introduction, you can't do better than Dateline NBC's Chris Hansen's "Mortgage Madness" special report. It was a pretty lengthy segment, but MSNBC.com has made the entire series available online. Watch the videos below in order.