For an industry that trades in the very, very small, projections about the potential scope of nanotechnology are gigantic. Estimates are that the industry will grow at a staggering pace in its first decade, reaching close to $3 trillion globally by 2014. The National Nanotechnology Initiative, created by President Bill Clinton in 2000, has called it "the next industrial revolution." Enthusiasts say that nanotechnology may someday enable scientists to build objects from the atom up, leading to entirely new replacement parts for failing bodies and minds. It may enable engineers to make things that never existed before, creating nanosize "carpenters" that can be programmed to construct anything, atom by atom -- including themselves. Or it may make things disappear, with nanowires that get draped around an object in a way that makes the whole package invisible to the naked eye.

As difficult as it is to comprehend how huge is the promise of nanotechnology, it's just as hard to wrap your head around just how tiny "nano" is. A nanometer is defined as one billionth of a meter, but what does that mean? The analogies are mind-boggling but not necessarily enlightening. Hearing how small things are when you're working at the nano level doesn't help you visualize anything, exactly; all it does is make you sit back and say, "Wow." If you think of a meter as the earth, goes one analogy, then a nanometer would be a marble. If you think of a meter as the distance from the earth to the sun, then a nanometer would be the length of a football field. A nanometer is one hundred-thousandth the width of a human hair. Or it is, in a particularly kinetic description, the length that a man's beard will grow in the time it takes him to lift a razor to his face.

"Things get complex down there, in terms of the physics and the chemistry," says Andrew Maynard, chief science adviser for the Project on Emerging Nanotechnologies, established in 2005 at the Woodrow Wilson International Center for Scholars in Washington, D.C., in partnership with the Pew Charitable Trust. "When you have small blocks of stuff, they behave differently than when you have large blocks of stuff."

At the nano level, some compounds shift from inert to active, from electrical insulators to conductors, from fragile to tough. They can become stronger, lighter, more resilient. These transformed properties are what account for the infinite potential applications of nanoparticles, defined as anything less than about 100 nanometers in diameter.

The field is a textbook example of exponential growth. According to Lux Research, an emerging-technologies research and advisory firm based in New York that has tracked the industry since 2001, the total value of all products worldwide that incorporated nanotechnology was $13 billion in 2004. That figure grew to $32 billion in 2005 and to $50 billion in 2006, and Lux Research projects it will reach $2.6 trillion by 2014.

Nanotechnology holds great potential for improving our lives. It might benefit the environment, for instance, by reducing our dependence on oil through the creation of a new power grid based on carbon nanotubes -- which can carry up to 1,000 times as much electricity as copper wiring without throwing off heat -- and solar energy farms that use thin, cheap, flexible nano-engineered solar panels.

Nanostructures offer better options for rechargeable batteries, for instance, including the ones to be used in the next generation of hybrid cars. One such battery, made with nanostructured lithium-iron- phosphate electrodes, is smaller and lighter, less environmentally toxic, and can hold more energy, take a charge more quickly, and maintain a charge longer than conventional lithium batteries, according to Michael Holman, a senior analyst with Lux Research. "It's not the compound itself that's nanoscale, but the surface of the material," Holman says. The surface of the battery electrode contains nanosize bumps and ridges, "which make the surface area much higher, allowing the electrons to flow in and out of it more quickly."

In the medical field, nanotechnology is expected to lead to dozens of innovations: new methods of cancer treatment that deliver chemotherapy directly to the tumor, earlier cancer detection using nanowires that can spot derangements in just a few protein cells, new methods of blood vessel grafting during heart surgery using nanoglue formed from nanospheres of silica coated in gold.

In cancer treatment, one application involves gold nanoshells: gold-coated glass spheres no more than 100 nanometers in diameter. These nanoshells enter tumors by slipping through tiny gaps in blood vessels that feed the malignancy. Once enough nanoshells accumulate in the tumor, scientists shine a near-infrared laser through the skin, heating up the gold particles and burning away the cancer. This technique, developed at the University of Texas Health Science Center, has worked in animal experiments and is about to be used in humans.

However, the real impact of nanotechnology, at least in the short term, will not be at the dramatic level of cancer cures or a new energy grid. For now, the technology will have to prove itself in the more mundane arena of commerce: washing machines that fight germs, antiseptic computer keyboards and kitchen utensils, windshields that repel the rain, sunscreens that rub on easily and block the full spectrum of ultraviolet rays. Nanoparticles are being put into stain-resistant clothing (Haggar NanoTex pants with NANO-PEL), super light tennis rackets (Wilson nCode), antiwrinkle face creams (Lancôme Rénergie Microlift), sunscreens (Blue Lizard), computer peripherals (IOGEAR), and a wall paint made by an Australian company, Nanovations, that says the paint can "achieve better energy ratings for buildings, better indoor air quality and fewer allergy-related illnesses."

But before we hurtle off toward a nano-utopia, we need to step back and ask ourselves whether this is a direction in which we really want to go.

When an industry grows this quickly, there may be neither the time nor the inclination to ask some tough questions about possible risks. First of all, there are the health and environmental hazards. Would nanotechnology bring unacceptable risks to workers making these materials or consumers who use the final products? Would it affect air or water quality near where the nanomaterials are dispersed? Very little is known about nanotoxicology, which might be very different from the toxicology of the same materials at normal scale (see "Smaller Is Weirder").