Three times a week, a group of strangers gathers in the basement of an independent New York City bookstore.

Their purpose? The volunteers—sometimes including tourists—pack more than 200 books a month, shipping them to prisons in 41 states. They belong to a collective called Books Through Bars, which provides reading material to inmates at their request.

Begun in Philadelphia roughly three decades ago, the collective sprouted chapters across the country, all operating on the same model: Books are donated to a partnering bookstore and volunteers match donations with requests.

ABC No Rio, an artist’s community center in Manhattan’s Lower East Side, started the work in 1996. Victoria Law, author of Resistance Behind Bars, is a founding member.

Prison reformers have long advocated more access to books for inmates. Research indicates that books and education ease the transition back into society, and reduce recidivism rates.

Odette, a volunteer with the Manhattan program, said that inmates are thankful such an organization exists. (She asked that her last name be omitted.) “In some cases, people may be cut off from family and friends, either due to solitary confinement or some other reason,” she said, “and we are one of the only forms of positive human contact they receive.”

The most requested items (and hardest to solicit donations for) are English- and Spanish-language dictionaries. Close behind are history books and titles on navigating the oft-confusing social services system.

Have titles you’d like to donate? Visit the Prison Book Program’s website for details on which program serves your state.