People in prison are always starving for books. A central aspect of survival in a cage is letting one's mind go elsewhere, continuing to learn, and often to organize. Keeping one's mind active, and as free as possible.
Programs like the Alabama Prison Arts & Education Project (run by a friend, I'm proud to say) are pioneering, and rare. This specific project is amazing in that it hasn't just built a library for inmates, it isn't just providing literature and art classes. It's political, and focuses on works by Southerners, by African Americans, by activists and prisoners. It's not a one-off, sending a James Patterson book and calling it a day. It provides context and support as well as inspiration.
Most prisoners are not in facilities with these kinds of programs. And that's why Books through Bars, Books behind Bars, Books to Prisoners, Prison Book Program, and many other similar organizations are invaluable in helping to fill the need.
Additionally, many independent bookstores and book trading services work with books-to-prison programs.
Please donate your books!