HABs are a worldwide concern affecting an increasing number of coastal ecosystems that result from the proliferation of a variety of noxious and toxic microscopic algae. In the U.S. almost every coastal state is now reporting recurring blooms. In the Recent activities by PICES, the West Coast Governors Agreement, and state/regional efforts have focused on HAB issues in the Eastern Pacific. This session seeks presentations on HAB monitoring and prediction efforts, comparisons within and between regions related to spatial and temporal patterns at all scales (i.e. fjords & estuaries versus open coast, range expansion, regime shifts, effects of climate change), and laboratory or field research related to better understanding of acute or chronic HAB events.