The Sea Grant Nonindigenous Species Site (SGNIS) is a national information center that contains a comprehensive collection of research publications and education materials produced by Sea Grant programs and other research institutions across the country on zebra mussels and other aquatic nuisance species. Materials available through this home page are classified as either peer reviewed or gray.  Peer reviewed materials have appeared in professional science journals or have been through a rigorous independent scientific review to ensure the quality of the information provided. Gray literature such as reports or proceedings that have not undergone peer review will be displayed with a gray background to distinguish it from the usual white background used for peer reviewed materials. We have added Outreach as a third section to SGNIS. This section contains science-based outreach products that have been reviewed for accuracy and are identified by a blue background.  Links are provided to other sites that focus on nonindigenous species.