The meeting aims at reviewing the basic concepts behind Naturally Occurring Asbestos (NOA), including the intended meaning of “fiber”, “asbestos”, "acicular crystal", and "fibrous mineral” and the sampling procedures to achieve reliable evaluation of NOA content in geo-environmental settings. Many issues are still unsolved in several steps of the “NOA evaluation task” (from sampling rocks on the field to the sample preparation techniques, from analytical observation and determination to hazard assessment) that require knowledge sharing from different working groups. The know-how gained in several case studies in Europe and US will be compared in order to focus on the most critical issues and to plan joined activities towards the definition of common best practices.