Abstract: In a bioeconomic framework to address the threat of invasive species there are two basic objectives: 1) to provide estimates of the regional economic impact an invasive species will potentially inflict upon a region; 2) to provide policy- makers with quantitative guidance for cost-effective alternative strategies to control, prevent, or slow the spread of the species. Within this framework I will address the spread of dreissenid mussels to the western U.S. and the spread of emerald ash borer in Ohio and Michigan. Recently, dreissenid mussels were discovered in the lower Colorado River. This infestation constituted the first population of dreissenid mussels west of the 100th Meridian and has the potential to increase their rate of spread in the western U.S. First, we forecasted the potential spread of dreissenid mussels throughout the entire United States by predicting the overland movement of recreational boaters with a production-constrained gravity model. Second, we used a computable general equilibrium model to determine the economic impact of a dreissenid introduction on the Columbia River basin. Our results predict that the relative probability of a dreissenid introduction to the Columbia River Basin has increased by ~25% compared to a previously published model based on the pre-Colorado invasion situation. Our economic analysis indicates that a dreissenid mussel invasion of the Columbia River Basin would result in a mean annual welfare loss of roughly $5 million. The emerald ash borer is poised to wipe out native ashes in North America with expected catastrophic losses to the ash tree forestry. To explore the bioeconomics of this invasion, we 1) estimated the potential 2) built a dispersal model incorporating both the ability of the emerald ash borer to spread naturally and via human-mediated dispersal 3) estimated the value of the ash industry using a computable general equilibrium model (CGE) and the potential direct costs to urban areas and 4) explored the costs and potential effectiveness of eradication efforts. Our results suggests the welfare loss to both Ohio and Michigan would be over $50 million annually, and that slowing the spread optimally would have cost over $1 billion. We hope our results will provide policy-makers with quantitative guidance for management of these invasive species.