Harold Evensky, a pioneer of the wealth management industry and one of my mentors (even though I've never met him - just read everything he's written and listened to him at conferences) has written a great piece on the what the subprime crisis really is.
In this paper Evensky details the inner workings of how the subprime mess started and what caused it. It's quite interesting and not to difficult to read.
If you've got a few minutes and are curious.....
Scott Dauenhauer, CFP, MSFP, AIF