Worldwide, millions of children are affected and made vulnerable by HIV and AIDS. Despite continued treatmentand prevention efforts, the number of orphans and vulnerable children (OVC) worldwide will likely increase, emphasizing theimportance of understanding the costs of OVC interventions. The USAID Health Policy Initiative, Task Order 1, applied two approaches to determine the costs of OVC interventions: for example, the project applied a microcosting approach in Ethiopia to estimate the cost per OVC reached with a specific service and a macrocosting approach in Cambodia to prepare national estimates of resources required to support OVC.