Scenario planning should be one of the Pentagon’s most important tools for developing strategy for an uncertain future. However, the formalized joint scenario planning process to support strategy and force development—Support for Strategic Analysis—has faced many challenges over the past 2 decades, and has ultimately proven less influential than intended on strategic decision-making. Explaining why is the main purpose of this monograph. It argues that scenario analysis has been most effective in supporting capability and program development, while it has fallen short in shaping strategy and force structure. The reasons for this are numerous and are rooted in intrinsic, structural characteristics of decision-making in large organizations. The monograph concludes with several recommendations for rejuvenating scenario planning in the Pentagon.