The Global Financing Facility (GFF), launched in 2015, is a partnership backed by a multi-donor World Bank trust fund that aims to prioritize and scale-up evidence-driven investments to improve reproductive, maternal, newborn, child, and adolescent health and nutrition (RMNCAH-N) interventions in low- and lower middle-income countries. A major component of the GFFs operational model is centered around the investment case, described by the GFF as a description of the changes that a country wants to see with regard to reproductive, maternal, newborn, child, and adolescent health (RMNCAH) and a prioritized set of investments required to achieve these results. Looking retrospectively at investment cases and associated ongoing World Bank operations, this paper aims to shed light on specific aspects of the GFFs operating model, approach, theory of change, and results to date related to the development of a costed and prioritized investment case, and whether the investment case helps to prioritize public spending on health in the real world.