Ex-U.S., or ex-United States, refers to an investment fund that specifically excludes shares or other securities issued by American companies. Because the U.S. represents so much of the global market capitalization, American investors who already own U.S equities can diversify geographically by buying ex-U.S. funds. If an American investor instead purchased a comprehensive global stocks fund, it would also include more U.S. stocks, effectively negating some of that diversification.