As one of the major vectors by which invasive species invade the coastal waterbodies and the Great Lakes, ballast water discharges from ocean-going ships are a major environmental threat to the Nation's waters. Recognizing the importance of ballast water as a vector for invasive species on a global scale, in February 2004 the text of an international ballast water treaty was negotiated through the International Maritime Organization (IMO). The IMO has proposed organism-based ballast water discharge standards for different size classes of organisms. While this represents a major accomplishment, there is concern that the IMO standards are not sufficiently protective. Accordingly, the United States Coast Guard (USCG) just released proposed Phase I (equal to the IMO standards) and Phase II (1000 more stringent then the IMO standards) standards for the waters of the United States. Additionally, California and other states have implemented or have proposed state standards more stringent than those proposed by the IMO. Historically, the EPA had excluded discharges incidental to the normal operation of vessels (including ballast water) from the need to obtain an NPDES permit. However, that exclusion from the NPDES permitting program was successfully challenged in court, and as a result, was vacated by the U.S. District Court for the Northern District of California. In light of the court decision, in December 2008 EPA issued a general NPDES permit (known as the 'Vessel General Permit' or 'VGP') that contains, among other things, standards for ballast water discharges from non-recreational vessels. The Office of Water currently is undertaking development of organism-based discharge standards for ballast water discharges for use in the future reissuance of the VGP. To help ensure it uses a scientifically sound approach in that effort, the Office of Water is seeking an objective and independent scientific opinion on approaches for deriving these standards and has requested that a National Academy of Sciences (NAS) expert panel evaluate the technical merits of approaches to generating the standards.