This book is about plants that have been introduced to new areas, usuallynew continents. It is about the attempts that have been made to charac-terize which introduced species will become serious weeds, about theirimpacts on native communities, and on how introduced weeds might becontrolled. Studies of invasive plants have provided a rich literature in ap-plied plant ecology. The invasion of plants into a new environment is anexample of succession in action and an experiment on the role of speciesin communities. In the following chapters we bring together theory andapplication to focus on both what the study of introduced plants revealsaboutecologicalprocessesandwhatecologicalprocessesmightbeappliedto management programs. We consider how community and populationecology can be brought to bear on the topic of invasive plants. Becausemany introduced plants become invasive and are considered to be weeds,we start here by defining weeds. Next, in this introductory chapter, wedescribe the socio-economic context surrounding introduced plants andintroduce topics to be discussed in more detail in following chapters