NYC Books Through Bars sends thousands of books to inmates across the U.S. each year. At the core of their work is the belief that education is a human right.

Twice a week, volunteers climb down the steep steps to the basement of Brooklyn’s Freebird Books. Once inside, they’re greeted by hundreds of books, stacks of brown paper bags and piles of letters. Before long, each book will be in the hands of an inmate somewhere in the U.S.

The cramped bookstore basement serves as the headquarters of NYC Books Through Bars, a volunteer-run group that sends books to incarcerated people in 40 states (the remaining states are either covered by similar programs or barred from receiving packages). In any given week the organization, which has been around for 21 years, receives hundreds of book requests: a Scrabble dictionary, a beginner’s guide to playing the guitar, a science-fiction novel — the list goes on. Each year, they ship somewhere between 10,000 and 12,000 volumes to federal and state prisons.

The U.S. incarcerates more people than any other developed country, with 10.6 million cycling in and out of the criminal justice system each year. Often, these prisons have libraries that are understocked and outdated. Others might not have a library at all, or at least not one that’s accessible to all inmates. New York’s infamous Rikers Island, for example, runs its library from a single cart. With roughly 8,000 inmates spread out among the complex’s 10 jails, getting your hands on even one book can feel like finding a treasure.

NYC Books Through Bars believes education is a fundamental right. It’s also one of the strongest tools to reduce recidivism — a 2013 study by the Rand Corporation found that educational intervention can lower a formerly incarcerated person’s chances of reoffending by about 40 percent.

But over the past decade prisons have cut back on educational programs, and inmates have been excluded from receiving Pell Grants, the financial-aid program for low-income college students, since the 1990s — all of which makes accessing educational support behind bars a challenge.

“In some instances, receiving a book is the beginning of an education,” says Daniel Schaffer, a collective member who’s been volunteering with NYC Books Through Bars for more than 16 years.

Instead of shipping donated books to a central prison library, the organization mails the titles directly to the inmates who request them, a novelty among programs offering similar services.

“Sending the books to the individuals adds to the strength of the project,” says Schaffer, adding that because some prisoners might not have families that visit, write or mail packages, NYC Books Through Bars might be the only contact they have with the outside world.

Schaffer stresses that a mailed book doesn’t reach just one person — inside a prison’s walls, books are passed around and shared.

Prisoners learn about the organization largely through word of mouth. And when one person hears about the books program, it’s just a matter of time before letters start arriving, Schaffer says. Sometimes they ask that a specific title be sent; other people are happy to receive anything from a particular genre. Among the most requested are dictionaries.

Because the books and packing materials are donated by the community, and Freebird lets the organization use its basement space for free, the program costs very little to operate. There are no paid employees, either. The only expense is postage, which is collected mostly through fundraising events. Even then, the organization cuts down on shipping costs by bundling four books in a package, at a rate of between $2.75 and $4.31 to ship.

Every Sunday and Monday, 10 to 20 volunteers collect, wrap and ship off the books. By the end of a three-hour shift, hundreds of brown parcels are stacked, ready to make their way to correctional facilities across the country.

Volunteers come from a range of backgrounds — students, librarians, archivists and editors among them — and not all hold the same beliefs about the current state of the criminal justice system. Some consider themselves abolitionists, while others promote reform. Still, everyone shows up for the same reason: to have an immediate effect on people on the inside.

“The thing that links everyone together, ultimately, is that we think the people who are in prison at least deserve to be treated as [humans],” Schaffer says.

“If, in an evening, I can do 20 or 30 or 40 books then that’s the number of individuals who are directly impacted,” he adds.

As requests for titles flood in to NYC Books Through Bars, so do the thank-yous. Letters, pop-up cards, drawings and other artwork from inmates line the shelves of the Freebird Books basement and get posted on Facebook. For the volunteers, the handmade tokens are a friendly reminder of the work they do.

Says Schaffer, “It helps to keep in mind that what you’re doing actually does impact people.”