FAS Nuclear Notebook
The FAS Nuclear Notebook is co-authored by Hans M. Kristensen and Matt Korda and published bi-monthly in the Bulletin of the Atomic Scientists. Each issue provides a snapshot of a nuclear-armed country weapons programs or a global nuclear weapons matter. The FAS Nuclear Notebook is one of the most widely sourced reference materials worldwide for reliable information about the status of nuclear weapons, and it is the most visited section of the Bulletin of the Atomic Scientists web site. Starting in 2020, the Bulletin only offers the Notebooks in web format, but full PDF formats are still available from Taylor & Francis. Because of their importance as a resource to an informed public debate about nuclear weapons, the FAS Nuclear Notebooks are freely available on the Internet.
The most recent FAS Nuclear Notebooks are listed below. Issues dating back to the very first issue in May 1987 can be found here (for missing early issues, see Google Books here):

Recent FAS Nuclear Notebooks:
May 2021: United Kingdom Nuclear Weapons, 2021
March 2021: Russian nuclear forces, 2021
January 2021: US nuclear forces, 2021
December 2020: Chinese nuclear forces, 2020
July 2020: Indian nuclear forces, 2020
March 2020: Russian nuclear forces, 2020
January 2020: United States nuclear forces, 2020
November 2019: US ballistic missile defenses, 2019
September 2019: Tactical nuclear weapons, 2019.
July 2019: Chinese nuclear forces, 2019.
May 2019: US nuclear forces, 2019.
March 2019: Russian nuclear forces, 2019
January 2019: French nuclear forces 2019
November 2018: Indian nuclear forces, 2018
September 2018: Pakistani nuclear forces, 2018
July 2018: Chinese nuclear forces, 2018.
May 2018: Russian nuclear forces, 2018.
March 2018: United States nuclear forces, 2018.
January 2018: North Korean nuclear capabilities, 2018.
November 2017: A history of U.S. nuclear weapons in South Korea.
September 2017: Worldwide deployments of nuclear weapons, 2017.
July 2017: Indian nuclear forces, 2017.
May 2016: [no Notebook this month]
March 2017: Russian Nuclear Forces, 2017 Because of frequent access problems with this issue, a backup copy is available here.
January 2017: United States Nuclear Forces, 2017
November 2016: Pakistani Nuclear Forces, 2016
September 2016: [no Notebook this month]
July 2016: Chinese Nuclear Forces, 2016
May 2016: Russian Nuclear Forces, 2016
March 2016: United States Nuclear Forces, 2016
January 2016: Declassified: US Nuclear Weapons at Sea During the Cold War
Older Nuclear Notebooks all the way back to the first issue in May 1987 can be found here (for those that are missing, see Google Books here). The FAS Nuclear Notebook is researched and produced by the analysts at the Federation of American Scientists. Previously it was produced by the Natural Resources Defense Council, headed by Robert S. Norris, and called the NRDC Nuclear Notebook.
The research that makes the FAS Nuclear Notebooks possible is generously supported by the John D. and Catherine T. MacArthur Foundation, the Ploughshares Fund, the New Land Foundation, and the Prospect Hill Foundation.