According to the National Association of Investors, one in three Americans feels "comfortable" investing in foreign stocks or bonds.

That, my friend, spells trouble
If this continues, we could be headed for some woeful underperformance, if not worse. Or so says the "smartest man in Europe."

The smartest who in what? That's what I said. But that's what Byron Wien calls him. According to Wien, this mysterious chap earned his title by consistently identifying trends that would have major impacts on global financial markets.

He even predicted the collapse of communism and the dismantling of the Berlin Wall, or so the story goes. And yes, he warned us to start looking for stocks abroad long before the historic bull market in foreign stocks.

You think I've lost my mind, don't you?
In my defense, I read this in The Washington Post, and Byron Wien is no hack. He was a top analyst at Morgan Stanley. So, I'm inclined to hear him out. As for his "mystery man" on the ground ... who cares? Just look at the numbers.

In 2005, stock markets in countries as diverse as Egypt, Russia, Turkey, South Korea, and Austria all gained 50% or more -- dwarfing U.S. stocks. The same thing happened in 2006, too. I don't know about you, but I'm starting to sense a long-term trend here.

In other words, we haven't missed the boat. In fact, when Wien last crossed the Atlantic to consult with his "source" on the ground, he was even more adamant that we'd be smart to move some of our investments overseas. For what it's worth, I'm taking him up on it.

"Global is definitely the way to go"
If you'd rather not trust your future to some "mystery man," how about a wizard from Wharton? When Professor Jeremy Siegel met with us here at Fool HQ last year, those were his exact words: "Global is definitely the way to go." Amazingly, Siegel suggests that we should hold as much as 40% of our portfolios in foreign stocks.

I wish I'd listened. I imagine some U.S. fund managers agree. Respected Vanguard U.S. Growth (VWUSX), for example, eked out a single-digit gain last year with hefty positions in U.S. stars like Genentech (NYSE:DNA) and Google (NASDAQ:GOOG), among other marquee names.

Not even a blowout finish from significant holdings Boeing (NYSE:BA) and Goldman Sachs (NYSE:GS) could get the fund within 20 percentage points of the return offered by the MSCI EAFE international index. But it could have been worse. At least the Vanguard finished in the green.

Too many American superstars, from Yahoo! (NASDAQ:YHOO) to General Electric (NYSE:GE), struggled to break even on the year. Clearly, like the rest of us, the fund could have benefited from a little foreign exposure. After all, international stocks and stock funds flat-out thumped their U.S. counterparts last year -- routinely delivering 20%-plus gains and, in many cases, much more.

Born on the fourth of July
I assure you: I'm not some doomsayer prophesizing the collapse of the West and the rise of "Chindia." I have too much faith in America for that ... and too much invested here in the U.S. markets.

But we can't deny the fact that more than half the total capitalization of public companies already resides overseas, and that just last year, investors poured $53 million into foreign large-company funds, up 32% from the year before. And, yes, I'm one of them.

So far, I've settled for that iShares EAFE Index. Because I confess: I'm out of my element investing in overseas stocks on my own. But I have a mystery man on the ground, too -- a Bill Mann, to be specific. If you don't know Bill, he's a longtime Fool, a globetrotter, and an expert on international markets. I won't invest a penny overseas without checking with Bill first.

Need some help, too?
Fortunately, you don't have to cross the Atlantic for good advice, either. Bill launched an investment newsletter service called Motley Fool Global Gains to help All-American investors like us take advantage.

If you already have some international experience, all the better. Bill's a serious expert. So, it's not exactly cheap to join. But that's what makes this so great. You can try the service free for 30 days and pay nothing. If you don't love it, don't join.

Of course, you won't actually go broke if you don't invest overseas. But it could cost you some serious money. Why not take Bill up on his free trial offer and try Global Gains instead? Already, since last November, Global Gains picks are up more than 25%. To learn more about this special trial, click here.

This article was originally published on Jan. 17, 2007. It has been updated.

Fool contributor Paul Elliott owns shares of the iShares EAFE index, but no other security mentioned. Yahoo! is a Motley Fool Stock Advisor recommendation. The Motley Fool has a disclosure policy.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.