This Conference took place from 26th to the 29th August 2009 at the national University of Ireland, Galway. It was organized to link our understanding of herring biology, population dynamics and exploitation in the context of ecosystem complexity. It is beyond argument that herring play a pivotal role in shaping the structure and dynamics of many boreal continental-shelf ecosystems. As fisheries management moves towards an ecosystem approach, the time seemed right for ICES to hold another herring symposium. Since the last ICES symposia on herring were in the 1960s (ICES Herring symposium, 1961; Biology of Early Stages and Recruitment Mechanisms of Herring, 1968) many of the former paradigms have been rejected and substantial progress has been made by striking out on new avenues of thought. In addressing this particular topic, we can also follow on from the decadal herring symposia series held in North America and thus cover new research from both the ICES and PICES community. It was fitting that this conference enjoyed the support of ICES, PICES and GLOBEC. Much has changed in the world of herring, since the last ICES symposium. Stocks have collapsed, recovered, and in some cases, have collapsed again. Work in recent years has focused on the development and evaluation of management strategies for herring stocks, and this work continues. The importance of herring in the food chain is an ever present consideration. Despite the many advances in our knowledge of stock structure and biology, herring population still present a challenge in terms of managing highly variable populations. We hope that this summary report, prepared by the science committee and the conveners, accurately represents the variety of presentations and discussions on this most variable of fishes.