Society is reliant on infrastructure services, such as information and communication technology, energy, water, and food supply, but also on governmental, cultural, and search and rescue organizations. The goal of project Kritis-KAT at the Federal Office of Civil Protection and Disaster Assistance in Germany is the development of generic criteria for the identification and evaluation of infrastructures regarded as "critical" for society. Acknowledging that full protection against all threats and cascading effects is not possible, the approach focuses on the impacts rather than the prevention of threats. The development of generic criteria requires the prioritization of infrastructures and identification of their key characteristics for civil protection purposes, risk management activities, and strategic proactive planning. For this purpose, the development of a national critical infrastructure priority inventory is based on a thorough examination of the range of criteria typically used in similar approaches. The specific focus of this paper is to identify and simplify essential characteristics of infrastructure criticality. The main outcome of this study is the development of common criteria generally applicable to a variety of infrastructures.