Quagga and zebra mussels are the most economically damaging aquatic organisms to invade the United States, costing an estimated $5 billion in prevention and control efforts since their arrival in the late 1980’s. Because of the threat posed by these invasive mussels to the Northwest, there is a compelling need to define and implement a region-wide prevention and response strategy. Recognizing this need, The Pacific NorthWest Economic Region, the Northwest Power and Conservation Council, Portland State University Center for Lakes and Reservoirs, and the Pacific States Marine Fisheries Commission sponsored a workshop on May 15, 2013 entitled, “Preventing an Invasion: Building a Regional Defense against Quagga and Zebra Mussels”. The workshop convened 90 individuals representing Canadian and Pacific Northwest irrigation and water districts, water suppliers, legislators, state and federal agencies, tribal sovereign nations, nonprofit organizations, recreational boating interests, consortiums, and others in Vancouver, Washington. The workshop developed a set of action items addressing the challenges and barriers to prevent the introduction of invasive mussels to the Pacific Northwest. The information on this website includes the presentations from the workshop and the action plan developed to address prevention efforts in the Pacific Northwest.