It’s been four years since international business consultant Todd Bol constructed a wooden replica of a one-room schoolhouse, filled it with books, and mounted it on a post in his front yard in a suburb of metropolitan Minneapolis, Hudson, Wis., in tribute to his late mother. A sign urged passersby to take free books or else leave books. Today, Bol and Rick Brooks, an instructor at the University of Wisconsin in Madison, head up the nonprofit organization Little Free Library, which promotes literacy through both sales and donations.

LFL has more than 5,000 registered structures in all 50 states and in approximately 40 countries. “We know there are many more than that,” Bol said, estimating there may be closer to 6,000 little free libraries at this point. “Many people build libraries and never register with us or tell us.”

The LFL movement has exploded in the last year, with 4,000 registrations in 2012 compared to 100 the previous year. While 90% of the libraries to date are in the U.S., and most library registrations have been made by individuals, with some businesses involved, Bol said that there’s been a recent shift: more public libraries, museums, schools, and other nonprofits are establishing partnerships with LFL. “I suspect we’ll double in under six months what we are doing,” Bol noted. “Our momentum is growing.”

Incorporated as a nonprofit last May, LFL grossed $50,000 in revenues in 2011 and $200,000 in 2012, enabling its two directors to begin taking salaries. Most of LFL’s revenue comes from the sale of the custom-made book containers, which are usually 23 in. wide, 16 in. deep, and 23 in. high. They range in price from $250 to $600. “Little Free Library” signs are also available for $60, and Little Free Library “stewards” pay $25 to register their locations. The registration includes a listing on LFL’s Google world map, accessible via its Web site. Library stewards may monitor the lending of books any way they wish; LFL provides stickers and bookplates that read “Always a gift, never for sale” that can be placed in the books.

LFL already has entered into partnerships with organizations that are taking the movement in new directions. For instance, LFL has partnered with Gaylord Brothers, a company that supplies furniture and archival products to public libraries, schools, and museums, to construct and market little free libraries with changeable panels on the roof and sides. Gaylord’s “artisan” libraries for the institutional market retail for $645–$755. “You can change the artwork, you can change the sponsors; [the artisan libraries] become thematic, ever-changing galleries that at the same time promote literacy and books,” Bol explained. “You can sell the same library [advertising and sponsorships] over and over again.”

The Minneapolis School District is also collaborating with LFL to establish a little library on every block in north Minneapolis, one of the most impoverished districts in the city. Ten little free libraries have been set up so far, with the school district hoping to have 100 libraries mounted in north Minneapolis by the end of the year.

Even the Mall of America has participated in the movement. Last summer, to celebrate its 20th anniversary, MOA sponsored the construction of 20 little free libraries, which were filled with books donated by various publishers, for LFL’s Little Free Libraries for Small Towns initiative. The initiative places little free libraries in rural parts of Minnesota and Wisconsin that lack public libraries. LFL is hoping to expand beyond these two states in the near future

Most recently, LFL has partnered with Books to Africa, a St. Paul, Minn.–based nonprofit that has been soliciting donations of textbooks and library books for Africa since 1988. LFL will design and build between 2,000 and 2,500 little libraries, with the costs defrayed by donations. After the libraries structures are shipped to African countries, they will be filled with books supplied by Books for Africa. Rotary International is dealing with the logistics of the distribution of the little free libraries. The first shipments of little libraries and books recently were sent to Ghana. LFL is also working on establishing partnerships with U.S. schools and libraries that are interested in communicating with classrooms and libraries in Africa to read and write books together.

“We’ll never get wealthy doing this,” Bol said. “But we’ve got so many cards and letters and e-mails saying the world is a better place because of LFL. The AARP said in their bulletin that LFL is revolutionary, similar to Oprah. She’d better call us!” —Claire Kirch