The decision to use a military intervention to achieve a political goal is inherently risky. To offset some of these risks, slates sometimes seek to build coalitions made up of partner states that have similar objectives. This report uses quantitative analysis and a series of qualitative case studies to identify and describe factors that seem to be associated with U.S. decisions to use coalitions for military interventions, factors that drive partner slates to join such coalitions, and factors that shape the success of military coalitions. The findings indicate that the United States relies on coalitions when operational demands are high and to build international legitimacy for military action. Partner states are most likely to join U.S. coalitions when they have close ties with me United States, when the precipitating crisis is in their home region, when they seek to advance their international standing, and when the coalition has support from an intergovernmental organization. As the United States faces more significant threats from near peer competitors, it may need to rely on partners more heavily and can leverage the insights in this report to construct strong and durable coalitions. Book jacket.