They stand in front yards, parks, health centers, and bus stops: small wooden boxes, each containing a stack of free books for neighbors to borrow. Todd Bol planted the first Free Little Library—painted to look like a miniature schoolhouse—outside his home in Hudson, Wisconsin. From there, the idea spread like wildfire. Today, stewards look after more than 6,000 libraries all across the country and around the globe, in spots as far-flung as Colombia and Pakistan.

Once the library is installed, it can become a locus of community-building and engagement as neighbors gather to exchange books and talk about what they've read. Some stewards say that within days of putting up their Little Free Libraries, they met more neighbors than they'd met in all their previous years of living in the community. In addition to the social aspect, the project encourages literacy by providing around-the-clock access to books.