The authors estimate that as of mid-2017, there are nearly 15,000 nuclear weapons in the world, located at some 107 sites in 14 countries. Roughly, 9400 of these weapons are in military arsenals; the remaining weapons are retired and awaiting dismantlement. Nearly 4000 are operationally available, and some 1800 are on high alert and ready for use on short notice. This article reviews the locations of nuclear weapons in all nine nuclear-armed states, as well as those of US weapons deployed outside the United States. The Nuclear Notebook is always free-to-access in our subscription Journal.