"There has been more material progress in the United States in the 20th century than there was in the entire world in all the previous centuries combined."
-- Stephen Moore and Julian Simon, Cato Institute, December 1999

Given the success of the 20th century, those of us living in the 21st century have come to expect constant improvements in technology. We expect to upgrade to a high-definition TV within a few years. We expect that our cell phones will soon also be our cameras, personal organizers, and portable music players. And, if you've seen the previews on YouTube, you expect to own a Microsoft Surface once it becomes available.

But this culture of constant expectation is a relatively new phenomenon in human history. In terms of technology, your great-great-grandfather's life in the 19th century wasn't that much different than his great-great-grandfather's before him. In fact, the two could have switched times and places and still functioned with relative ease. But try putting one of them here in the 21st century. Talk about a fish out of water! Things we accept as commonplace today -- commercial airplanes, television, and microwaves -- would be downright perplexing to them.

And to think, all of these world-changing advances took place in just the 20th century. Heck, in just 66 years we went from the Wright brothers' first flight to Neil Armstrong setting foot on the moon. That's absolutely incredible when you think about it in the context of human history.

So, what's next?
If the first seven years of this century are any indication, 21st-century innovation will prove to be even more prolific than that of the 20th. Consider this: More than 100 million Apple (Nasdaq: AAPL) iPods have been sold since 2001 and have forever changed the way we listen to music. And nearly 17 million people now subscribe to satellite radio services XM Satellite Radio (Nasdaq: XMSR) and Sirius Satellite Radio (Nasdaq: SIRI) combined.

And those are just consumer products. Rapid technological advances are also being made in the health-care and renewable-energy industries. In 2006, for instance, Atripla, the once-a-day HIV-fighting pill from Gilead Sciences (Nasdaq: GILD) and Bristol Myers Squibb (NYSE: BMY), received FDA approval. Atripla stands to simplify dosing schedules and increase viral suppression of an affliction that affects more than 39 million people worldwide.

A recurring topic that will be addressed and re-addressed in the 21st century is the need for renewable energy sources. Integrated oil companies are getting into the renewable-energy game. BP (NYSE: BP), for example, recently announced its intention to invest $8 billion in solar, wind, natural gas, and hydrogen fuel technologies.

Clearly, whether the eventual solution is wind energy, ethanol, nuclear energy, a more efficient use of current fossil fuels, or solar energy, a lot of money will be spent and made to solve our world's growing energy needs. At our Motley Fool Rule Breakers growth-investing service, one company we've recommended is Suntech Power (NYSE: STP), a Chinese company that designs, manufactures, and sells photovoltaic cells, which are used to generate power in solar panels. Currently, solar power accounts for a small fraction of current energy use, so there's huge growth potential here. Moreover, because Suntech is aiming to be the world's low-cost producer of solar technology, our Rule Breakers team thinks the company is in a good position to meet both consumer and environmental demands.

How to profit from change
More world-changing technology will come about in the 21st century than in any previous period. The Cato Institute's report noted that "the progress of the 20th century is not a mere historical blip but rather the start of a long-term trend of improved life on earth." Indeed, science and engineering have already reshaped the world we knew just 10 years ago.

This is great news for investors. Such innovation presents unparalleled opportunities to capitalize on the pioneering companies that will change our world, but which of these companies are worthy of your investing dollars?

Fool co-founder David Gardner and his Rule Breakers team are always keeping their eyes out for ground-breaking companies that also happen to have great business models. If you'd like to see the team's picks, including their top five ideas for new money, just follow this link for information on a free 30-day trial.

This article was originally published Oct. 16, 2006. It has been updated.

Fool contributor Todd Wenning does not own shares of any company mentioned. Microsoft is a Motley Fool Inside Value pick. The Motley Fool is investors writing for investors.