Smoking bans -- in airplanes, offices and restaurants -- were designed to reduce the public's exposure to dangerous second-hand smoke. But it turns out the restrictions do much more than that: they reduce smoking overall.
"When you make workplaces, public places, restaurants and bars smoke-free, people smoke less," said Dr. Stanton Glantz, director of the Center for Tobacco Control Research and Education at the University of California, San Francisco. "They sell fewer cigarettes."
Smoking bans increase the stigma and hassle of smoking, and remove some of the social cues for lighting up. Workplace bans, especially, can have a dramatic effect.
"We've consistently found that you get a 30 percent drop in cigarette consumption when you make a workplace smoke-free," Glantz said. "About half of that is people cutting down and about half of it is [people] quitting."
David Spalding smoked for more than 20 years. He quit 3 1/2 years ago after his employer, Blue Cross/Blue Shield of Minnesota, went entirely smoke-free.
"I believe without the ban and my employer, I'd still be smoking today," he said. "I didn't want to be driving off campus to have a cigarette in a car. It was that simple. And that was my catalyst."
Spalding wasn't the only one.
"When we started the policy, about 18 percent of our employees smoked, and a year after the policy had been in place, the smoking rate was at 15 percent," said the company's vice president, Dr. Marc Manley.
There is evidence that restrictions work in public places as well.
More than 2,000 cities and counties now have laws that restrict indoor smoking.
In New York City, the number of adult smokers fell by 500,000 in four years, in part because of smoking bans in restaurants, bars and offices.
More than 680 cities also place some restrictions on smoking outdoors as well.
In San Francisco, studies concluded that smoking bans helped drop the lung cancer rate by 6 percent. City parks then became smoke-free, and so have many California beaches.
Hundreds of cities no longer allow smoking at building entrances. There's even been talk of banning smoking in private cars when children are present.
Critics of government-imposed smoking bans worry what comes next.
"Is this a form of spousal abuse to smoke around your spouse? If you have pets, is this a form of cruelty to animals?" said Jacob Sullum, senior editor of Reason magazine.
The fight over smoking bans continues in many parts of the country. Bars and casinos are the biggest battleground. They are often the last refuge of smokers who want to light up inside.
Dover Downs casino in Delaware was forced to limit smoking by a state law; it is allowed only in a separate lounge. Like many business owners, they worried about a decline in customers.
But a 2004 study in California, Connecticut, Delaware, Maine and New York -- states with smoking restrictions -- showed no significant change in restaurant and bar revenues.
Now at Dover Downs, business is booming.
"Well, at first there were fewer people because the smokers were sort of rebelling, but now they're back," said patron Auga Fitch.
Smoking bans are gaining popularity, even at home. Studies in California and Massachusetts show nearly half of all smokers ban smoking in their houses.
Gretchen Morrison is one of them.
"It's not just the smell and the stench," she said. "It's for health reasons, also."
Morrision says her home smoking ban has forced her to cut back. She hopes it will help her quit to live.
ABC News' Lisa Stark filed this report for "World News Tonight."