The usual rules apply at the Boston Public Library’s central branch: No loud voices in the book stacks. But the building is hardly quiet. On any given day, it’s bustling with people attending the library’s many public events—children’s story time; movie screenings; book clubs; and classes and workshops on computer skills, résumé writing, and podcasting. Others come for the daily art and architecture tours, which take visitors through the 1895 building, designed by architect Charles Follen McKim of the prominent firm McKim, Mead and White, and its Modernist 1972 addition by Philip Johnson. For Bostonians, this institution—the first free municipal library in the United States—plays many roles.

“A lot of people thought the Internet would destroy [public] libraries, but really, they’re more vital than ever in communities,” says Kenneth Breisch, founder of what is now the University of Southern California School of Architecture’s Master of Heritage Conservation program and author of American Libraries 1730–1950, published by W.W. Norton in September 2017.

And while Google may have replaced the Dewey Decimal System as the preferred research tool, many public libraries have found ways to grow and adapt. For instance, two years ago, the Boston Public Library’s central branch completed a multiyear, $78 million renovation led by William Rawn Associates. The project included a new, high-tech community learning center, a state-of-the-art welcome center, and a cafe.

“Libraries really are more than just places to get books,” Breisch says. “They’re community and cultural centers.”

Businessman and philanthropist Andrew Carnegie saw early on the importance of libraries as community centers. Carnegie was a self-educated man who believed he owed much of his success to the library he frequented in his youth after moving to Pennsylvania from Scotland. He made donations of more than $40 million from the late 1800s to 1919 to build more than 1,600 libraries in the United States, urging each one he funded to have a community center or auditorium where people could gather.

The first Carnegie library to open its doors was the Braddock Carnegie Library in Braddock, Pennsylvania, a Romanesque structure designed by William Halsey Wood. It was in continuous use from its dedication in 1889 until 1974, when major structural issues led to its closure. The library was slated for demolition until a group of Braddock residents formed the Braddock’s Field Historical Society, purchased the building for $1, and began restoring it. In 1983 it reopened and has served as a vital community hub ever since.

Carnegie libraries are often among the oldest surviving buildings in towns across the country, Breisch says. And while many have been converted into museums, city offices, or other spaces, plenty still loan out books today. They vary in size, from the majestic Italian Renaissance–style Detroit Public Library designed by Cass Gilbert in 1921, to smaller ones, such as Mirror Lake Community Library in St. Petersburg, Florida (a Beaux-Arts structure built in 1915 and expanded in 1997), and the Carnegie Public Library in Big Timber, Montana (a one-story, Neoclassical brick building constructed in 1913 and renovated and expanded in 2007).

Though many of America’s earliest public libraries are traditional brick or stone structures, midcentury architects began taking these institutions in new stylistic directions. James W. Hammond of Skidmore, Owings & Merrill designed the angular, 34,200-square-foot Skokie Public Library in Skokie, Illinois, in 1960. Three years later, the American Institute of Architects and the American Library Association recognized the building with a design award. It’s been expanded twice in its 58-year history to increase capacity and programming options.

And in Orlando, Florida, architect John M. Johansen designed the Orlando Public Library, a concrete Brutalist building dedicated in 1966. It was expanded and renovated two decades later, and in 2014 it opened a 26,000-square-foot digital technology center on the second floor, complete with audio studios and 3-D printers.

Similar expansions and high-tech offerings have come to many of the New York Public Library system’s 88 neighborhood branches, more than a third of which were established by a $5.2 million grant from Andrew Carnegie in 1901. Filmmaker Frederick Wiseman celebrates the branches’ ever-expanding roles in his 2017 documentary, Ex Libris, which explores how, for many New Yorkers, the neighborhood library is an extension of their homes.

“I would argue public libraries are the most democratic spaces in America today,” Breisch says. “Everybody’s welcome.”