Microscopic planktonic algae are the basis of the ocean’s food chains supporting fisheries and aquaculture, however algal blooms can also have negative effects (aka red tides), causing widespread mortality of marine life. Of the more than 5000 phytoplankton species less than 10% bloom to densities of more than 1 million per liter and only 1% have the ability to produce harmful toxins killing marine organisms and in some cases humans. Worldwide there has been an increase in frequency, intensity and geographic extent of harmful algal blooms (HABs) as seen in the number of cases of paralytic shellfish poisonings in 1970 compared with 1990 (Hallegraeff 1993). There are a number of potential hypotheses that have been proposed to explain the increase in HABs including, increased scientific awareness of toxic species, increased utilization of coastal waters and fisheries, increased transport of dinoflagellate resting cysts, stimulation of plankton blooms by eutrophication and/or changing oceanographic conditions. Studies of HABs and toxic dinoflagellates have a number of challenges including the scarcity of phytoplankton surveys, poor taxonomic information, difficulties culturing toxic species and changes in the toxin production of phyotoplankton. In this symposium we invite scientists working on HABs in the California Current to present results from their work as well as make recommendations for ways to move HAB research forward. We anticipate that this symposium will bring the long-term oceanographic sampling tradition of CalCOFI and the HAB research communities together to enhance collaboration, survey planning, data sharing, prediction capabilities and funding opportunities.