The Laurentian Great Lakes have been the primary site of establishment for many nonindigenous species in North America, and have acted as the beachhead for invasions of other drainage systems.  We are focusing efforts on preventing the introduction of potentially harmful species because once species are established the prospects for eradication are limited.   To this end we are analyzing ship movement data to determine the role different source ports, vessels, and visitation frequency have played in primary invasions.  Results will be used to identify priority vessels for intervention, and to predict identity and source location of future invaders.  For species established in the Great Lakes, recreational boating appears to be the most important vector of spread to new watersheds. We have surveyed boaters to determine patterns of travel and behavior, and are experimenting with different techniques to reduce rates of spread. Finally, sampling from the trades in live organisms has demonstrated that this is also an important vector for primary and secondary invasions.  Proactive policies that remove known and potential invaders from these trades would reduce future invasions.  Together this research demonstrates that simple management and policy approaches could greatly reduce future impacts of Great Lakes invaders.