After more than a century since sea otters (Enhydra lutris) were nearly hunted to extinction, and subsequent protection and intensive management, sea otter populations are recovering at varying rates across their historic range. USGS has been actively engaged for decades conducting research addressing sea otter recovery, constraints to recovery, and ecosystem consequences of growing abundance of this keystone species. This talk will present ongoing and new research to measure and understand status of sea otters in California and Alaska, obstacles to further population growth or recovery, and questions surrounding the potential of future reintroductions. It also highlights the collaboration across USGS regions that has led to a broader understanding of sea otter population ecology.