Considerable uncertainty persists about the resources required to implement public health programs and policies, and about the factors that drive variation in resource needs and utilization across community and institutional settings. This paper reviews several alternative approaches to cost estimation that we have used in the field of public health services & systems research (PHSSR). This review was prepared for an expert panel meeting convened as part of a study commissioned by the U.S. Assistant Secretary for Planning and Evaluation (ASPE) to estimate the costs associated with public health emergency preparedness capabilities.