This chapter examines the science diplomacy of Norway and Finland to mitigate SLCPs, in particular black carbon emissions. For Norway, we focus on the science diplomacy initiatives towards China, and for Finland, towards Russia. These initiatives involve different combinations of governmental actors alongside various public and private sector actors in research, development and innovation (RDI). We assume that such diplomacy succeeds better if the actors are driven by similar interests and can arrive at shared problem definitions. In the Norwegian-Russian case, a bilateral research programme was launched, facilitating the convergence of interests and problem definitions on the part of both governmental and RDI actors on both sides. In the Finnish-Russian case, no similar vehicle existed connecting the high-level diplomacy initiated by the president of Finland with the country’s RDI cluster, and the actors on the Russian side with largely different interests and problem definitions. Finland’s ambitious initiative was further hampered by the Russian interests in this area mostly pertaining to adaptation rather than to mitigation, and by Russia’s full-scale invasion of Ukraine since February 2022 that thwarted the prospects of using the Arctic regional co-operation track in support of the Finnish efforts.