Theme Invasion biology is still a young ecological sub-discipline, but it already starts to show signs of age and its development is losing pace. Until recently, new concepts on invasive species were proposed on a monthly basis, and there was great excitement about finding new patterns and explaining them. More and more data have become available on invasive species which, however, often question existing concepts. For example, the results of small-scale experimental studies are sometimes in conflict with the results of large-scale observational field studies, as is the case for the biotic resistance hypothesis. Some researchers also argue that many concepts cannot be tested at all, as for example data on the number of introduced species are typically unreliable. Broad concepts additionally have difficulties to capture differences among individual invasion events. As a consequence, the list of well-supported concepts on invasive species is awfully short. Invasion biology has entered its next stage, a stage that might be termed “crisis”. Parts of the Workshop Part A: Is there an emerging crisis of invasion biology? We invite contributions (talks or posters) that identify concepts of invasion biology and show how well they are supported by theoretical or empirical evidence. Your contribution can be purely theoretical or based on modeling, a meta-analysis, a review, experiments, or field studies within any taxonomic group. Contributions setting the problems of invasion biology into a philosophical context are also highly welcome. Part B: How can we achieve major progress? We appreciate contributions here that suggest solutions to invasion biology’s problems. For example, you may (a) suggest how existing untestable concepts have to be modified to be-come testable, (b) identify necessary methods and data to validate testable concepts, or (c) pre-sent your ideas on how to develop novel concepts with broader but well defined extent and scope. In this second part of the workshop, we will also form sub-groups to discuss different possible solutions to invasion biology’s problems. Each sub-group will present its results to the other workshop participants in the concluding overall discussion. If interesting insights are achieved, all participants are invited to contribute to a joint publication that summarizes these insights