In parallel to rapid sea-ice loss and other climate impacts in the Arctic Ocean, large-scale changes are now apparent in northern landscapes and associated ecosystems. Arctic communities are increasingly vulnerable to these changes, including effects on food security, water quality, and land-based transport. The project “Terrestrial Multidisciplinary distributed Observatories for the Study of Arctic Connections” (T-MOSAiC) was conducted under the auspices of the International Arctic Science Committee over the period 2017-2022. The aim was to generate multiauthored syntheses, protocols, and observations toward an improved understanding of Arctic terrestrial change, and to identify priorities for northern research, monitoring, and policy development. This special collection of Arctic Science covers a broad range of these themes, including limnological insights into northern lakes and rivers, a set of protocols for permafrost and vegetation monitoring, an integrated perspective on Arctic roads and railways to bridge the social and natural sciences, snow and ice studies at the coastal margin of the Last Ice Area, and Indigenous perspectives on Arctic and global conservation. The contributions summarized in this introductory article to the T-MOSAiC special collection include recommendations for the future, and they illustrate the immense value of Arctic collaborations that bring together researchers across disciplines, nations, and cultures.