The Institute for Defense Analyses (IDA) has assisted the Korean Institute for Defense Analyses (KIDA) in identification of international best practices in defense strategy, planning, and resource management. As part of this effort, this document identifies international best practices for defense planning scenarios, and in particular, their usage in the United Kingdom (UK) and United States. It defines scenarios; specifies their role in supporting defense management decisions; identifies best practices for the development and management of scenarios; and examines their role in the UK and United States. Finally, there is an in-depth analysis of KIDA’s approach to scenarios using the identified international best practices with specific recommendations for improvement in the approach, scenario construction, and scenario management.