In 1947, the seemingly everyday, innocent thoughts of a teen girl were published. But they weren’t so everyday: they were the thoughts of Anne Frank, a 13-year-old in a unique position to help the world understand what it was like to have to hide your entire existence in exchange for a mere chance at surviving the Nazi regime.

Her diary has since sold more than 30 million copies and has been translated into 67 languages. If you haven’t read The Diary of a Young Girl in a while (or even if you have), here are 10 things you should know about the book and its author, who—along with her family—was captured by the Nazi Gestapo on August 4, 1944.

1. The “diary” Anne received for her 13th birthday was actually an autograph book.

The aspiring writer decided it would be better used as a journal. She switched to two notebooks after the autograph book was full, and finally resorted to about 360 pages of loose leaf paper.

2. Anne wrote most of her diary in the form of letters to a person named “Kitty.”

So who was Kitty? Scholars are divided. Some believe “Kitty” refers to Anne’s prewar friend, Käthe "Kitty" Egyedi. Others disagree, believing that Anne borrowed the name from her favorite book series, Joop ter Heul, in which the title character’s best friend was named Kitty. Egyedi, who survived the Theresienstadt concentration camp, later said that she did not believe the letters were meant for her.

Not all of the diary was addressed to Kitty, by the way. Early letters were also addressed to Conny, Marianne, Emmy, and Pop.

3. Anne and her family were found when they were betrayed by someone—anonymous to this day—who knew where they were hiding.

German officers raided the building and made arrests on August 4, 1944. The arresting officer, Karl Silberbauer, later said he vividly remembered arresting the Franks, and even reportedly told Otto Frank, “What a lovely daughter you have.” When Silberbauer’s actions were discovered in 1963, he was suspended from his job at the Viennese police force. He is quoted as saying, “Why pick on me after all these years? I only did my duty. Now I am suspended and I have just bought some new furniture and how am I going to pay for it?" After an investigation, he was allowed to return to his job.

Silberbauer also later admitted that he bought a copy of The Diary of a Young Girl to see if he had been featured. He wasn’t. “Maybe I should have picked it up off the floor,” he said.

4. Anne died in Bergen-Belsen concentration camp, but not in the gas chambers.

Emaciated, she had already lost her mother to starvation, her sister to typhus, and believed her father to be dead. For a long time it was believed that three days after her sister’s death, Anne herself succumbed to typhus in March 1945—and that the camp was liberated by British troops a few weeks later. But in 2015, new research released by the Anne Frank House suggested that both Anne and her sister, Margot, may have died in February (one month earlier than was previously believed).

5. Of the eight people who had been hiding in the Secret Annex, only one survived.

Otto Frank, Anne’s father, survived Auschwitz and was liberated by Soviet soldiers in January 1945. By summer, he learned that his daughters and his wife were all dead. It was Otto who published Anne's diary in 1947. Otto went on to have a long life: he passed away in Basel, Switzerland in 1980, at the age of 91.

6. Otto Frank was given Anne’s diary by Miep Gies, one of the Dutch citizens who helped hide the Franks.

Miep Gies collected the diaries and papers after soldiers left and hoped to be able to return them to Anne one day. After receiving the pages, Otto submitted them for publication, knowing that was what Anne had intended. The first edition of the diary was called Het Achterhuis, or The Secret Annex.

7. Had Miep Gies looked at the contents of the diary, we never would have gotten to read Anne’s innermost thoughts.

Gies later said that if she had known what was inside, she would have destroyed the writings because they incriminated everyone who helped hide the Franks, the van Pels, and Fritz Pfeffer. Otto Frank finally persuaded her to read it when the book was in its second printing.

8. The Diary of a Young Girl is often banned and challenged.

Anne Frank's writing has caused some controversy over the years, but not for the reasons you might think. There are passages in the diary in which Anne expresses curiosity about her anatomy—a totally normal thing for a girl in her teens to do. In fact, the passage is more humorous than “pornographic,” as some protesters have called it:

"There are little folds of skin all over the place, you can hardly find it. The little hole underneath is so terribly small that I simply can't imagine how a man can get in there, let alone how a whole baby can get out!"

9. One Alabama school tried to ban the book for a very dumb reason.

In 1983, a school in Alabama tried to block Anne’s diary from schools simply because it was “a real downer.”

10. Some people—mostly Holocaust deniers—believe that Anne Frank’s diary is a forgery.

In an effort to put these rumors to rest, the documents were analyzed for handwriting, glue and binding methods, and the types of ink and paper. Nothing was found that would even remotely point to the diary being a fake.

This story has been updated for 2019.