Mutual funds, like stocks and bonds, are very common investment instruments among large and small investors alike. When you buy shares of a fund, you become part owner – along with other fund investors - of a large investment portfolio made up of hundreds or even thousands of individual securities issuers. A professional investment advisor manages the fund's investments according to its stated objectives, for instance, long-term growth, current income, etc. The diversification inherent in so many separate issuers within a single fund works to sharply curtail the risk of serious loss due to the underperformance of any one company or industry.