(FORTUNE Magazine) – PRACTICAL INNOVATION--FROM THE STEAM engine to the search engine--is the principal reason America achieved preeminence while other well-endowed land masses lagged or failed. Innovation is not simply invention, something to be measured by the number of patents or shrieks of "Eureka!" in the lonely lab. It is inventiveness put to use. As Thomas Edison admonished his associates, "We've got to come up with something. We can't be like those German professors who spend their whole lives studying the fuzz on a bee."

The myth of Alexander Graham Bell is illustrative. He was no innovator. He was the discoverer of how sound waves could be converted to undulating electric current. It was certainly a marvelous moment on the evening of March 10, 1876, when his young assistant Thomas Watson heard Bell's voice down the wire: "Mr. Watson, come here. I want you!" But as Watson later remarked, the Bell phone was calculated more to develop the American voice and lungs than to facilitate conversation. It was left to Edison (with Charles Batchelor) to produce an effective carbon-button microphone so that when Western Union pooled the patents of Edison and Bell's rival Elisha Gray, it had a real working telephone. Then Theodore Vail presided over the amalgamation of Western Union and the Bell Telephone Co. to create the American Telephone & Telegraph Co. Vail foresaw the potential of a long-distance system and worked to overcome myriad political, technical, and bureaucratic obstacles. The innovator of the telephone was Vail. (He was also founder of the research facility that in 1925 became Bell Labs.)

Chester Carlson was like Bell. He fooled with static electricity and cooked up chemicals on his kitchen stove in Queens in 1938 to transfer a dry mark from one piece of paper to another. No commercial organization was interested. The Battelle Memorial Institute in Columbus took the invention a stage further starting in 1944. Joseph C. Wilson, new to the presidency of his father's Haloid Corp., a maker of photography products, sent his friend Sol M. Linowitz, a public-spirited lawyer just out of the Navy, to look at it. "We went to Columbus to see a piece of metal rubbed with a cat's tail," said Linowitz. From 1947 to 1960, Wilson invested $75 million in the device, taking his company to the brink of extinction. Wilson was the innovator of the Xerox machine.

Invention without innovation is a pastime. Some inventors, like Edison, do follow through from an inspiration to its fulfillment in society. We have FM radio only because inventor Edwin Armstrong was ready to go into the marketplace himself in 1939 after RCA chief David Sarnoff blocked FM for fear it would destroy his income from the manufacture of AM radios. But many innovators could not invent a tin whistle.

Here, then, is the defining characteristic of the innovator: a determination to bring a brainwave into the bustle of the marketplace.

Dedication to introducing something new carries with it a readiness to take risks for a vision--and to suffer contumely for doing so. The experience of almost all the men and women I've studied in researching my new book, They Made America, suggests that the principal quality of an innovator lies less in the cortex than in the epidermis. An innovator without a thick skin will fail, because anyone advocating change is invariably pursued by swarms of stinging naysayers. Raymond Damadian was a "screaming lunatic" for thinking nuclear magnetic resonance imaging might be used for medical diagnosis. Theodore Judah was "crazy Judah" for advocating a railway over the high Sierras. Amadeo Giannini was a "hothead dago" for setting up branch banking for the masses: Bank of America was the result. Having triumphantly spliced a gene, the young molecular biologist Herbert Boyer endured academic opprobrium by going into business to mass-produce man-made hormones; synthetic insulin and Genentech were the sequel.

New ideas arouse the "if it ain't broke, don't fix it" dogmatists in large corporations. Such bureaucrats never remember their predictions when success is achieved, but since nothing works the first time--think CNN or Amazon.com--they often think they've been proved right. Innovators who make it have a maddening characteristic: They are obsessive. Often an idea works only when pressed beyond its sensible limits. Samuel Insull and Juan Trippe demanded engines of unheard-of power for, respectively, electricity generation and aircraft. Half-way measures would not have yielded ever-cheaper power for decades of industrialization or affordable fares on a Pan Am 747 to Europe.

"Indomitable perseverance in a business properly understood always ensures ultimate success," Cyrus McCormick wrote. Though the evidence is not totally conclusive, perseverance does seem more significant than originality. Consider two great raw materials, oil and rubber. There is argument about who first thought drilling might find oil, but there can be no question that only the pigheadedness of Edwin Drake led to the famous bonanza in Titusville, Pa., in 1859--after all the men-of-the-world investors had capitulated. Young, illiterate Nathaniel Hayward was on the right track in 1838 to unlock the mystery of how raw rubber might be rendered usable, but he gave up like everyone else. It was Charles Goodyear who took Hayward's insight and brought it to fruition--going in and out of jail for debt all his life and sacrificing his family on the altar of vulcanized rubber.

More innovations come from borrowing and combining than from simple invention. "I invented nothing new," said Henry Ford. "I simply assembled into a car the discoveries of other men behind whom were centuries of work." It sounds easy, but it emphasizes another quality more significant than originality: imagination as manifest in the ability to see relationships. Lewis Tappan did not start the first credit agency; it was his fusion of earlier ideas that led to Dun & Bradstreet. Jean Nidetch did not invent the diet she used for Weight Watchers; she made it effective by borrowing the mutual-support techniques of Alcoholics Anonymous. Ruth Handler based Barbie on a German sex doll named Lilli but transformed a static doll into a vehicle for role modeling when she offered a variety of outfits--an idea itself stolen from cardboard cut-out games. "Good artists borrow; great artists steal," said Picasso, who may have lifted the quote from someplace else.

Innovators come from all segments of society and flourish in America's mobile, egalitarian ethos. It gives a flavor of where lightning strikes to mention that the principal creators of America's economic revolutions include a trucker, a portrait painter, a cobbler, a Harvard professor, a deck boy, a fruit wholesaler, a drug dealer, a hairdresser, a peddler, a billboard salesman, a miller, an illiterate daughter of slaves, a '60s rebel on the streets of San Francisco, a beach taxi pilot, a seamstress, a piano salesman, a foreman in a power plant, a U.S. Navy seaman with nothing to do on a warship at the end of World War II, a playboy, a radio ham, a clerk, and of course a couple of bicycle mechanics.

The cynicism of the great French realist Honoré de Balzac ("Behind every great fortune there is a crime") is vindicated less than one might expect. A willingness to sacrifice family (Goodyear, Edison) or betray partners (Isaac Singer, Sam Colt, and Collis Potter Huntington are in Olympian class) is not uncommon. But a surprising number of history's innovators have a redeeming virtue. They wanted to enhance our lives, to make it possible for the whole population to enjoy goods and services previously available only to the elite. Giannini did that with his branch banking for the little man, Ford with his Model T, George Eastman with photography. The young programming genius Gary Kildall and engineer Ken Olsen extended access to the computer beyond a select priesthood. Pierre Omidyar created a democracy of supply and demand with eBay. In Reno, Raymond Smith transformed casinos from dark, smoky rooms peopled by men to public places of entertainment, foreshadowing the rise of Las Vegas.

Some may say that this is a romantic illusion, that these democratizers were merely catering to the masses for the sake of higher profits. None of them, to be sure, sought penury in the service of the public, but my immersion in the lives of innovators over several years has left me convinced that moneymaking was not a sustaining motivation. A desire to be God's agent in the service of mankind was uppermost in the actions of Morse, Vail, Tappan, Judah, Olsen, and Martha Matilda Harper (beauty parlors). Giannini positively turned his back on wealth ("No man owns a fortune; it owns him"). The ever-pragmatic Ford insisted, "Thinking first of money instead of work brings on fear and blocks every avenue of success."

In all the innovators I call democratizers, altruism was no doubt diluted by vanity, the desire to be acclaimed as a benefactor, to be acknowledged by one's professional peers--and there is nothing wrong with that. But the extra zip and zest in American innovation springs less from "robber baron" greed than from a democratizing instinct intrinsic to the republic.