Technical Abstract: Piñon-juniper is one of the major vegetation types in western North America. It covers a huge area, provides many resources and ecosystem services, and is of great management concern. Management of piñon-juniper vegetation has been hindered in the past by inadequate understanding of its prehistoric and historic dynamics, of the mechanisms controlling those dynamics, and of the variability in ecosystem structure and process that exists among the many different environmental contexts and floristic combinations of piñon, juniper and associated species. This paper presents a summary of what we currently know – and don’t know – about historical and modern stand and landscape structure and dynamics, in three major and fundamentally different kinds of piñon-juniper vegetation in the western U.S.: persistent woodlands, savannas, and wooded shrublands. It is the product of a workshop that brought together experts from across the geographical range of piñon-juniper vegetation. The intent of this synthesis is to provide a source of information for managers and policy-makers, and to stimulate researchers to address the most important unanswered questions.