Keys to Investing in Mutual Funds (Barron's Business Keys) (ISBN 0812096444)

Amazon.com Review:
Few investments are as widely appealing as mutual funds. They permit individuals--including those with limited knowledge of financial markets, those planning relatively small commitments, and those seeking long-term fiscal stability--to join larger groups purchasing a variety of securities managed by experienced professionals. These investments, however, should never be made blindly, and this new edition of Warren Boroson's Keys To Investing in Mutual Funds explains everything necessary to understand all the benefits and risks.

May be dated, but a useful primer:
This is an excellent book to get a good overview of what mutual funds are and why they are such a good investment vehicle for many people. Written in a lively, engaging style, it lays out in brief chapters essential concepts in easy-to-understand language. While it is now dated, it is still a great place to start.