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 March 1973, his wife Sally M. Conly and daughter Jane Leslie Conly completed the work, guided by his notes. Set in the continental territory of the United States, it is written from the first-person perspective as the diary of sixteen-year-old Ann Burden. Burden has survived nuclear war and nerve gas by living in a small valley with a self-contained weather system.