At this Third WMO Workshop the key recent results in all these areas were presented and discussed. The Workshop’s agenda covered three major sections including Global Forecast Impact Studies, Regional Aspects of Impact Studies, Observation Targeting Studies and Observation Network Design Studies, where 30 lectures were presented. Almost 50 experts representing all major NWP and other centres active in the area of observing system impact studies, as well as representatives of the CGC Management Group and the WMO Secretariat attended the Workshop. The programme of the Workshop and the list of participants are given in Annexes I and II respectively. The full text of papers presented at the Workshop as provided by the authors are reproduced in the second part of the Proceedings.