The SIPRI Yearbook is an authoritative and independent source of data and analysis on armaments, disarmament and international security. It provides an overview of developments in international security, military expenditure, weapons and technology, arms production and the arms trade, armed conflict and conflict management, and efforts to control conventional, nuclear, chemical and biological weapons.This 55th edition of the SIPRI Yearbook covers developments during 2023, including-Armed conflict and conflict management, including an overview of global and regional developments in armed conflicts, peace processes and peace operations, along with thematic sections on the role of Russian private military and security companies, food insecurity, and climate-related peace and security risks in Yemen -Military expenditure, international arms transfers and developments in arms production, including the consequences of the Russia-Ukraine war and ongoing geopolitical tensions-World nuclear forces, with an overview of each of the nine nuclear-armed states and their nuclear modernization programmes-Nuclear arms control, covering the dialogues involving China, Russia and the United States and within multilateral treaties, as well as the response to Iran's nuclear programme and attacks on Ukrainian nuclear power plants-Chemical, biological and health security threats, including the investigations of allegations of chemical and biological weapon use and developments in the international legal instruments against chemical and biological warfare -Conventional arms control and regulation of inhumane weapons, with a focus on the use of explosive weapons in the Russia-Ukraine and Israel-Hamas wars, as well as the consequences of missile proliferation and the collapse of the Treaty on Conventional Armed Forces in Europe-International governance of artificial intelligence, cyberspace and space security, with a focus on autonomous weapon systems-Dual-use and arms trade controls, including developments in the Arms Trade Treaty, multilateral arms embargoes and export control regimes, and the legal framework of the European Union for such controls It also contains updated annexes listing arms control and disarmament agreements, international security cooperation bodies, and key events in 2023.