Stranger in a Strange Land is a pro-religion, anti-theist book about free love and the Sapir-Whorf hypothesis, and was controversial even when it was published in 1962.
So naturally it was challenged as part of the curriculum of a summer "Science Academy" course in Texas.
The book was actually retained after a 2003 challenge in Mercedes, TX to the book’s adult themes. However, parents were subsequently given more control over what their child was assigned to read in class, a common school board response to a challenge.
NOTE: Not part of censorship, but an interesting story none the less:
According to one biography, Heinlein started off in his early career and with his first wife, Leslyn, as a Left-wing New Dealer with an open marriage and an open mind, but somewhere along the line his politics shifted far to the right. He and his first wife divorced and he wed Virginia whose politics were close to what his had become. This explains in part the dichotomy of his writings: Starship Troopers hardly has the same philosophy as Stranger In A Strange Land.
It has often been said that Heinlein and his friend L. Ron Hubbard had a contest. One of them would write about religion, the other would start a religion, and they would see which one did better with his project. Heinlein wrote Stranger In A Strange Land; Hubbard founded the Church of Scientology. It didn’t quite end there.
As it turns out, Heinlein inadvertently did both. A group of folks who had read Stranger In A Strange Land took the religion founded by Valentine Michael Smith to heart and the Church of All Worlds stepped off the pages of the novel into a real-life religion. Its founders, Oberon (Otter) and Morning Glory Zell took it well into the 21st Century, though Morning Glory Zell passed away earlier this year.
All in all, this novel was considered by no less than the Library of Congress to have been one of the books that shaped America, having had a profound effect on our lives. It is also one of the few novels to be available both in the original, edited edition and also in the form that the author had originally wanted it, which is about a third longer. Make up your own mind which version is better.