A defect criticality framework and assessment procedure for composite material systems has been proposed, based on the multi-level assessment philosophy contained within API (American Petroleum Industry) 579 - Recommended Practice for Fitness-For-Service and Continued Operation of Equipment. The basis for the framework detailed in this guide is a 3 Level approach which involves increasing levels of sophistication in the assessment approach, from operator to expert. For each level, guidance and recommendations have been provided as to the degree of knowledge and complexity required for non-destructive evaluation (NDE), defect classification, defect criticality assessment and materials characterisation.Four industrial case studies have been undertaken in order to demonstrate various aspects of the framework and to validate the approach proposed.