Policymakers are increasingly seeking to determine whether the federal government's recent investments in public health preparedness have left the public health system better prepared to respond to large-scale public health emergencies. Yet, there remain questions about how to define "public health emergency preparedness," how much preparedness is enough, and how preparedness can be measured and assessed. This chapter identifies the key challenges associated with measuring public health preparedness and reviews approaches currently in use. We also identify some emerging measurement techniques that might help address some of these challenges.