Z for Zachariah is a post-apocalyptic science-fiction novel by Robert C. O'Brien that was published posthumously in 1974. The name Robert C. O'Brien was the pen name used by Robert Leslie Conly. After the author's death in 1973, his wife Sally M. Conly and daughter Jane Leslie Conly completed the book guided by his notes. Set in the United States, the story is in the form of a diary written from the first-person perspective of sixteen-year-old Ann Burden, who has survived a nuclear war and nerve gas through living in a small valley with a self-contained weather system.