An excellent reference to understand financial futures; an easy-to-read book with minimum or non technical stuff. Shall be a good reference for undergraduate derivatives courses. It clearly explains the way repos and reverse repos are performed, an important issue to understand the behavior of interest rates and the nowadays (2009) tests done by the Federal Reserve as a matter of its monetary policy.
If you want to do better in financial derivatives, you should have this book in your shelf (but be sure to read it not only store it).