Estimates of the costs of implementing health interventions are required for informing a wide range of decisions in global health. Costs are used in economic evaluations, such as benefit-cost or cost-effectiveness analysis, and other economic analyses to inform priority setting. Cost interventions are also needed for financial planning and management, and the formulation of resource requirements and budgets. In addition, cost estimates can provide additional detail on how interventions are implemented, which can be useful for assessing the efficiency of service delivery. Costs are typically estimated using a range of approaches and assumptions, often combining data obtained as part of research studies with data collected as part of routine program implementation. While numerous textbooks and guideline documents exist, analysts apply and interpret such guidance based on their prior training, professional experience, and context. However, there is no widely agreed-upon common guidance on principles, methods, and reporting standards specifically aimed at cost estimation across global health. The variation in applying the methods and reporting of costs for global health interventions has long been recognized. This variation can have an impact on estimates of cost-effectiveness, which should be comparable across interventions. A review of economic evaluations in the Tufts Medical Center Cost-Effectiveness Analysis (CEA) Registry found a high level of variation in costing methods, although the review noted an improvement in consistency over time. Differences in data collection methods and in the application of analytic methods, a general lack of comprehensiveness, and inconsistent compliance to existing guidance were all observed. As a result, reviews of global health costs conclude that methodological heterogeneity and lack of transparency make it impossible to compare studies over setting and time, and several papers point to the need to develop standardized methods for cost estimation in global health.