Associate Professor David Letts AM CSM has authored a chapter, 'Intelligence sharing among coalition forces', that appears in National Security Intelligence and Ethics (Routledge, 2021). Since the end of World War II, there have been numerous examples of coalition operations involving two or more military forces, including some operations that have been held under the authority of the United Nations through the passing of a UN Security Council Resolution. 1 Other types of multinational operations, comprising both formal alliances that are set up under treaty arrangements, such as NATO, 2 and more informal coalitions that are typically established under ad hoc arrangements that deal with a specific issue or incident, such as the International Maritime Security Construct, 3 have been a feature of military operations for centuries. 4 Changes in the structure of alliances and coalitions have also been a regular occurrence, often driven by changes that occur in the political landscape of one or more partner State. There are also other types of cooperation that occur between military forces, such as routine participation in exercises and training activities, as well as exchange of personnel, staff meetings and high-level discussions between senior officials. Overall, these activities are all examples of two or more foreign militaries working together to achieve a common objective.