Vanguard Prime Money Market Fund seeks to provide current income and preserve shareholders’ principal investment by maintaining a share price of $1. As such it is considered one of the most conservative investment options offered by Vanguard. Although the fund invests in short-term, high-quality securities, the amount of income that a shareholder may receive will be largely dependent on the current interest-rate environment. Investors who have a short-term savings goal and seek a competitive yield may wish to consider this option.