Invasive species are a leading threat to aquatic biodiversity and ecosystems. Because invasions are among the most irreversible of human impacts, prevention is the most important approach for dealing with this problem. But with approximately 15,000 lakes in Wisconsin, how do we focus our efforts most effectively? We have been working with a variety of researchers on what we call 'smart prevention' projects. The idea is to identify lakes that are most likely to be invaded and most likely to be impacted by an invader.These 'vulnerable' lakes can be mapped using Geographic Information Systems (GIS) to show the pattern of vulnerability on the landscape, and prevention and monitoring efforts can be directed to these vulnerable sites. This type of analyses has been conducted for bass invasions in Ontario lakes, and is presently being conducted on rusty crayfish, rainbow smelt, round goby, zebra mussel, and spiny water flea in Wisconsin.