Invasions of introduced species cause varying degrees of harm on the ecosystems in question and it is up to society to deal with the consequences. How can we prevent biological invasions? How can we assess the risk they represent? What can be done to control current invasions? Aware of this problem, the Ministry of Ecology has requested a community of researchers from a variety of disciplines to decipher these questions using biological, sociological and economic approaches. Although the definitive response to the problems raised by invasive species in natural spaces is not provided here, undeniable progress in understanding mechanisms underlying these invasions can shed light on the decisions which have to be taken by environmental managers. Scientists, teachers and students will also find results and thought-processes in this book to supplement their knowledge.