A framework for benchmarking a future data centerís operational performance is essential for effective planning and decision making. Currently available criticality or tier methods do not provide defensible specifications for validating data center performance. An appropriate specification for data center criticality should provide unambiguous defensible language for the design and installation of a data center. This paper analyzes and compares existing tier methods, describes how to choose a criticality level, and proposes a defensible data center criticality specification. Maintaining a data centerís criticality is also discussed.