In 2009, Tod Bol built the first Little Free Library in the Mississippi River town of Hudson, Wisconsin, as a tribute to his mother—a dedicated reader and former schoolteacher. When he saw the people of his community gathering around it like a neighborhood water cooler, exchanging conversation as well as books, he knew he wanted to take his simple idea farther.

“We have a natural sense of wanting to be connected, but there are so many things that push us apart,” Bol says. “I think Little Free Libraries open the door to conversations we want to have with each other.”

Since then, his idea has become a full-fledged movement, spreading from state to state and country to country. There are now 18,000 of the little structures around the world, located in each of the 50 states and in 70 countries—from Ukraine to Uganda, Italy to Japan. They’re multiplying so quickly, in fact, that the understaffed and underfunded nonprofit struggle to keep its world map up to date.

Khalid and Yasmin Ansari, who live in Qatar, say they get a special satisfaction out of seeing their six-year-old son Umayr’s Little Free Library represented on the website. “When looking at the LFL world map,” says Khalid, “you almost feel obliged to have one in the neighborhood to fill the gap. It's like doing your part in your part of the world.”

In some places, Little Free Libraries are filling a role usually served by brick-and-mortar libraries; the organization’s Books Around the Block program, for example, aims to bring LFLs to places where kids and adults don’t have easy access to books. In North Minneapolis, an area more often in the news for shootings than community engagement, the Books Around the Block initiative set up 40 of the little libraries. Two hundred more sprung up shortly thereafter.

Last year, Sarah Maxey of Winston-Salem, North Carolina, discovered Little Free Libraries when browsing the crowdfunding site Kickstarter. She was then inspired to launch her own LFL Kickstarter campaign. The response was enthusiastic: By the time the campaign ended, Maxey had raised more than $10,000 for her cause—enough money to build dozens (and dozens) of little libraries.

“What happens is, you start the momentum, and then the community—the Lions Club, the Rotary, the churches, the neighbors—steps up and builds more. It just keeps going,” Bol says.

Individual stewards are using their Little Free Libraries in altruistic ways, too. Tina Sipula of Clare House, a food pantry in Bloomington, Illinois, does more than distribute groceries; she distributes books via an on-site Little Free Library. As she points out, homeless people don’t have addresses—which means they can’t get public library cards. Linda Prout was instrumental in bringing dozens of Little Free Libraries to New Orleans after Hurricane Katrina, and Lisa Heydlauff of Bihar, India, is working to bring a thousand Little Free Libraries to girls’ schools in her country, filling them with books that teach business and entrepreneurial skills.