This document is the overarching standard for the provision of private security services for critical infrastructure. It is complemented by vertical substandards for specific sectors with more detailed focus on the related services such as e.g. aviation security and maritime/port security. It specifies service requirements for quality in organization, processes, personnel and management of a security service provider and/or its independent branches and establishments under commercial law and trade as a provider with regard to security services. It lays down quality criteria for the delivery of security services requested by public and private clients. This document is suitable for the selection, attribution, awarding and reviewing of the most suitable provider of security services.