In 2018, the California Legislature adopted a pair of bills that require the State to begin building microplastics management strategies for both drinking water and California's aquatic ecosystems. The passing of these bills initiated a burst of collaborative activity in California to provide a scientific foundation for these legislative mandates. For instance, multiple international efforts have been convened to identify the primary pathways by which microplastics affect aquatic biota and humans, prioritize the microplastic characteristics that are of greatest biological concern, develop frameworks for assessing the risks associated with microplastics, and identify critical thresholds at which those biological effects become pronounced. In addition, methods for both sample collection and analysis have been evaluated to better understand method performance and work toward standardization. Through these activities and others, critical research needs were also identified, laying the groundwork for the next phase of microplastic research and environmental management in California.