The Polar Research Board, in collaboration with the Board on Life Sciences of the National Academies of Sciences, Engineering, and Medicine, convened a workshop in December 2018 to discuss vegetation greening and browning in tundra and boreal ecosystems. Studies have often documented large-scale greening trends (i.e. increased plant productivity and measured “greenness”) but they have also identified areas of browning (decreased productivity) or shifts between greening and browning over varying spatial extents and time periods. These findings have fueled many questions about observed trends and identified drivers, implications of vegetation change, and methods and tools for evaluating changes and their uncertainties. These topical areas formed the primary themes of the workshop and were discussed by experts representing remote sensing and field-based research communities from U.S. and international institutions.