This volume contains the papers and abstracts of the posters given at the symposium on Long-term Changes in Coastal Benthic Communities organized by the Commission of the European Communities in Brussels, Belgium from 9 till 12 December 1985. The organization of this symposium came to conclude five years of activities in the COST 647 project on Coastal Benthic Ecology, the rationale of which is explained in the foreword by B. F. Keegan. The importance of this volume is that for the first time special attention is given to long-term data series of relevant biological variables collected in different marine benthic habitats. Many of the data presented here are the result of years of careful data collection by some of the leading scientists in the field of benthic ecology. Some of the series, such as the Macoma balthica data from the Wadden Sea or the macrofauna data from Loch Linnhe, to name just those two, are already classics in the marine biological literature. Other data were collected in the framework of a monitoring programme and are now analyzed for the first time in the different perspective of the COST 647 project. Several papers are from related fields where they represent well known case studies; they were chosen in order to see how problems have been tackled elsewhere.