Paralytic shellfish poisoning (PSP) is a recurrent and widespread problem in the Gulf of Maine (GOM) caused by the dinoflagellate Alexandrium fundyense. Blooms of this species have been the subject of more than a decade of investigation through the ECOHAB-GOM and GOMTOX research programs. Multiple large-scale field surveys have provided data that were combined with mooring observations, satellite-tracked drifters, and numerical model simulations to document the complex dynamics of A. fundyense blooms within this region. A detailed conceptual model of A. fundyense bloom dynamics and PSP toxicity in the region is summarized here, highlighting where possible the key physiological, behavioral, and environmental or oceanographic factors involved. A numerical model has also been developed and evaluated against cruise observations and other data. The status of those modeling efforts is discussed, including recent efforts to provide seasonal forecasts of Alexandrium bloom magnitude, and near-real time hindcasts and forecasts of use to resource managers.