In February 1905, a Chicago lawyer named Paul Harris founded a business and fellowship club for men. He called it the Rotary Club, and its aim was to promote the friendly, cooperative spirit of small-town America. The Club was an immediate success.

From the beginning, says current president Glenn Estess, Rotarians "found that really to fulfill their desires they had to do more than just meet, and eat together and fellowship. So they started this avenue of trying to serve those who were in need."

Today, as the group now known as Rotary International marks its centennial, its membership exceeds 1 million, and its vision of small-town fellowship is being shared throughout the world.

"In 1917, the president of that year suggested that we ought to start a fund to do good in the world," says Mr. Estess. "Out of that evolved the Rotary Foundation, which is now the world's largest privately funded scholarship fund."

Rotary -- which was so named because the location of its meetings rotated among members' offices -- quickly spread throughout the United States and beyond.

Jeffrey Charles is the author of a book about the history of Rotary and other private service clubs in American society -- groups like the Kiwanis and Lions Clubs. Mr. Charles believes Rotary has been successful in the United States because it addressed the needs of changing communities.

"Many small cities and towns found themselves left behind. Their economies were changing," Mr. Charles says. "The business elite in the community was fracturing, with some becoming corporate, others remaining small local businesses, and Rotary helped them come together to overcome the split that was really tearing some of these business communities apart.

Mr. Charles says Rotary enjoys a generally positive public image today -- although it hasn't always been so. The organization drew criticism for its associations with fascist Germany before the World War II. And while it accepted black members even as America struggled with racial segregation during the 1950s, all-male Rotary Clubs didn't offer membership to women until the 1980s.

Today, Rotary International has developed a progressive reputation by funding programs designed to spur economic and social development in the world's poorest countries.

There are now about 33,000 Rotary clubs in 168 countries. The clubs work in their individual communities and support other clubs in broader efforts, including literacy promotion, village health projects, tsunami relief in Southern Asia, supporting AIDS orphans, combating hunger, and preventing malaria and river-blindness.

Rotary is perhaps best known for its pledge, 20 years ago, to help immunize all the world's children against polio, a crippling viral disease. It has worked in partnership with international groups such as the U.N.'s World Health Organization.

Rotary International President Glenn Estess says the effort to eradicate polio has made tremendous progress. "We embarked on that program in the 1985 -1986 era, and at that point, there were about 1,000 cases of polio a day being reported," he says. "Over the years, Rotarians and their friends have immunized about 2 billion children. And the number of cases at the end of 2004 was less than 1,300 cases worldwide."

Mr. Estess says Rotary is currently working with the government in Indonesia to immunize an additional 5 million children.

Some of Rotary's projects are uniquely challenging. The president-elect of the Washington D.C. rotary club, Andy Cook, says his group is partnering with Rotary clubs in Tokyo and other Asian capitals to help organize the removal of land mines from the former battlefields of Southeast Asia.

Mr. Cook says the extensive worldwide partnership of Rotary Clubs gives the organization a special advantage when responding to international crises. "Where we differ from other organizations (is that) we have people on the ground -- locals who are Rotarians and are able to help," he says. "So if you're an outside organization, you may have to work, for instance, to get transportation, but with us, the Rotary clubs, the members will have their cars. If we need to get relief, they can organize their pickup trucks to bring relief to the site. In that sense, we are sometimes able to hurdle obstacles that other organizations are not able to."

And Mr. Cook believes the enduring appeal of the Rotary Club is that it brings members of a local community together, while including them in a larger organization, where they can have a worldwide impact.

Rotary's centennial observance culminated this month when some 40,000 people from around the world turned out for the club's annual convention in Chicago, the city where Rotary began, 100 years ago.