The genus Prorocentrum includes six planktonic species that form high-biomass blooms, and at least nine predominantly benthic toxigenic species. Four of the plankters, including P. minimum, the only plankter reported to be toxigenic, are among the most commonly recognized harmful algae that are increasing in frequency, duration, and magnitude globally. Growth studies suggest a species group that ... [Show full abstract] generally grows maximally at inorganic nutrient N:P ratios just below Redfield proportions. However, field studies indicate that planktonic Prorocentrum species bloom when nutrients are at high N:P ratios relative to Redfield proportions. In the benthic species P. lima complex, toxin production has been shown to be inversely related to nutrient limitation, increasing when nutrient ratios are above Redfield proportions. Mixotrophy and allelopathy can play an important role in the interactions among planktonic Prorocentrum species, diatoms and other dinoflagellates, but little information is available for benthic taxa. The available information suggests that there are allelopathic interactions among benthic species and other algae, and that benthic species also can adversely affect finfish and shellfish health. While high growth rates may allow blooms of the plankters to initiate blooms, adaptive physiology is hypothesized to allow blooms to be maintained at less than maximal growth rates and at non-optimal N:P ratios. Given the projection for increasing land-based nutrient export to continue, it is expected that there will be further expansion of planktonic harmful Prorocentrum spp. globally and more intensive or more toxic benthic occurrences in the future.