As countries drive towards achieving high and equitable coverage of life-saving vaccines, the availability of sustainable, equitable, and predictable financing for vaccine delivery is essential. Over the last two decades, great strides have been made in expanding the coverage of routine and new vaccines, in part through better understanding the cost of delivering immunization services. However, gaps in cost evidence remain, such as the costs associated with different delivery strategies, the cost of scaling up, and the upstream drivers of immunization delivery costs. In addition, the data that do exist are often fragmented, of variable quality, and/or difficult to access and use by policymakers, program planners, and other global and country-level stakeholders. Consequently, historical funding levels, rather than cost evidence, are often used to plan and budget immunization programs.