A true “natural” forest can be defined as an idealized virgin forest condition that is uninfluenced by large-scale, systematic human activity; yet human activities have been so widespread and taken place over such a long period of time that there is probably little, if any, strictly natural forest remaining on planet Earth. Nevertheless it is a valuable exercise to reconstruct as many properties of natural forest as possible in the boreal and temperate zones to provide a reference for conservation, restoration, and silviculture and to help identify the best examples of near natural forests throughout these biomes. Near-natural forests are important research sites for both conservation biologists and silviculturalists. All silvicultural systems are modifications of natural systems to a greater or lesser extent, and studies of the dynamic processes within natural forest can serve as guidelines and as sources of inspiration for the development of “close-to-nature” silvicultural systems (Bradshaw et al. 1994; Larsen and Nielsen 2007). As society and forest managers seek systems that safeguard ecosystem services such as biodiversity and minimize long-term environmental impact, it seems helpful to reexamine the concept of natural and its realization in reference sites. In this chapter, I review the probable broad-scale distribution of natural forest within the boreal and temperate zones and discuss some of the defining characteristics of natural forest and the fresh insight into the history of natural forest stands provided by the recent application of molecular biological techniques to forest genetics, species composition and CONTENTS