This chapter provides the first overview of the disruptive impacts of HABs on the blue economy, with a particular focus on the application of science and technology in their management and mitigation. We present case studies of HABs in five different locations as examples of their effects on different sectors of the blue economy. We also review the main technological advances in recent decades, and current needs for improved understanding of HAB dynamics, monitoring, and forecasting. An evident gap in dealing with HABs in the frame of the blue economy is the inequity in resources available for monitoring worldwide. While developed countries count on advanced (and even impressive) tools for monitoring and early warning (e.g., automated tools, oceanographic moored instruments, forecast models), efficient monitoring in most developing countries is still missing and, when performed, mainly focused on seafood products intended for export. Basic research on HABs in these countries is also frequently deficient, with modeling capabilities for early warning virtually non-existent. Considering that many (truly) sustainable blue economy activities are developed precisely in vulnerable areas with low economic power, the need for the development of affordable and sustainable technologies becomes critical, allowing for the efficient monitoring of HABs.