The present document defines and describes a set of Key Performance Security Indicators (KPSI) to be used for the evaluation of the performance@ the maturity levels of the detection tools and processes used within organizations for security assurance. The response is not included in the scope of the present document. In particular@ the purpose of the present document is to enable organizations to: assess the overall maturity level of the security event detection; provide a reckoning formula to assess detection levels of major security events as summarized in GS ISI 001-1 [1]; evaluate the results of measurements. This work is mainly based on the US SANS CAG [5]. The target groups of the present document are Head of detection@ reaction teams@ Cyber defence team and head of security governance.