This book presents a study of existing cases of informal international law-making and seeks to propose a code of conduct for State Nuclear Command, Control and Communication (NC3).As the threat of nuclear escalation rises with increasingly fractious situations in Ukraine, Taiwan, and the Middle East, the risk of accidental or illegal deployment of nuclear weapons is likewise escalating. Experts in security studies have long called for better clarification on best practice in State NC3. This study explores how each nuclear weapons State structures (and should structure) its NC3 and what international law governs nuclear operations. Given the lack of international law regarding NC3, this book argues that it would be beneficial to adopt a code of conduct or other non-binding instrument outlining any law regarding nuclear weapons operations, including any best practice regarding how States should structure their NC3 systems, given their strategic and policy objectives. In proposing a model code of conduct, this study will examine the existing literature and practice on the adoption and implementation of non-binding instruments in the international law of armed conflict, to better understand how and why non-binding instruments gain traction in State practice. The final chapter will then apply those conclusions to a draft code of conduct for State NC3.This book will be of interest to scholars and practitioners of international law and security studies and a valuable resource for those working in the field of nuclear command, control, and communication in government and in civil society.