My first brush with mailroom censors came when I was in a county jail in upstate New York in the winter of 2010. After almost a decade of struggling with heroin addiction, I’d gotten arrested just a few days before I was supposed to finish my last semester at Cornell.

I’d never been in jail before, and once I realized that the typical cellblock routine included a whole lot of nothing, I told myself I would use the long, empty hours to work on one of the few remaining papers I needed to graduate. I could do something productive to get my life back on track, I thought, while also distracting myself from the enormity of my mistakes and the looming threat of prison time.

Luckily, I had family to support me, and they offered to send in my (admittedly voluminous) notes for the paper. But there was a problem: The paper was an analysis of World War II propaganda — so my notes consisted of hundreds of index cards filled with descriptions of Nazi films.

The jail staff did not allow me to have them — but not because of the Nazi content. White supremacy was fine, apparently. Notecards, however, were not.

At the time, I found it hilariously bizarre. But now, more than a decade later, I write about incarceration for a living, so I know that such absurdities are common. Many prison systems ban reading materials because of their formats: No hardbacks! No pop-ups! But often, it’s the content they object to — except when they don’t. Only a handful of prison systems ban Adolf Hitler’s “Mein Kampf.”

For almost a year, The Marshall Project has been collecting lists and policies in the hopes of publishing a database of all the books that corrections departments block incarcerated people from owning.

This week, we got as close as we could. Our tool includes banned titles in 18 states, and we will add more over time. As with a lot of data that comes out of prisons, there were problems. One state didn’t respond to my records requests at all. A handful sent unusable, messy data. And about half of states — as well as the Federal Bureau of Prisons — said they don’t keep lists.

Instead, authorities in those states often evaluate each publication as it comes in — meaning that a book rejected at one prison may be permitted at another, or a book that is banned one month could be allowed in the next. The procedures in states which do have banned books lists often start when the mailroom staff at one prison flag an incoming book (often ordered online by a prisoner’s friends or family members), then refer it to a review committee or a higher-ranking official to decide whether it should be prohibited statewide.

Read the full article about prison book bans by Keri Blakinger at The Marshall Project.