"For those who support and believe in the power of international law to effect positive change in the world, 2019 was difficult. There were however a number of important bright sparks, in the form of efforts to negotiate treaties on the protection of marine biodiversity, business and human rights, and the elimination of work place harassment; as well as spotlights shone by national and international courts on the plight of some of the world’s most vulnerable people. The past 12 months have both highlighted the political limits within which international law operates, and the good it can achieve within those boundaries. This post reflects on some of the most important new cases, treaties, and events; as well as the international legal order’s most difficult challenges. 1) Climate change and loss of biodiversity accelerate Climate emergency is Oxford’s word of the year and, as we are closing out the warmest decade on record, evidence of global warming seemed to be everywhere. The ferocity of forest fires both in the Amazon and in areas of Australia, fuelled by extreme drought, are but one worrying example. They also illustrate the limits of international law’s ability to force change on governments who are unwilling to accept it. Against this dark backdrop, the 2015 Paris Agreement’s achievements look modest. Climate change poses an existential challenge to international law, in that it affects almost everything it regulates. International cooperation is our only hope of tackling it, but it is difficult not to question whether the existing international legal architecture is up to the challenge..."