Today dead trees are not only viewed upon as waste and as potential sources of pest species. Instead they have gained an increased attention as key factors for biodiversity in many ecosystems. This change in focus and concern has sparked intense research activities directed to explore the ecological role of dead trees in forest ecosystems. Focus is directed into three main areas: 1) to understand the patterns of woody debris availability in relation to forest stand dynamics and effects of forestry, 2) the role of woody debris in nutrient and particularly carbon dynamics in forest ecosystems, and 3) the pattern and biology of the utilization of woody debris for a large number of wood-dependent species. This volume summarises the present knowledge and presents a set of case studies on the role of dead wood in boreal forests. The focus is on Fennoscandian boreal forests. However, the results presented have a wide applicability and thus the volume may serve as a general introduction to the importance of woody debris in forest ecosystems.