The Paris Climate Agreement represents a landmark for international efforts to mitigate and adapt to climate change. 195 countries agreed to an international treaty with universal participation, ambitious objectives, and robust processes and rules to ensure implementation and a continuous strengthening of action against climate change. However, the Paris Agreement represents a potential that is still to be realised. One of the most crucial provisions of the Paris Agreement that remains to be elaborated is the call on all countries to develop “long-term low greenhouse gas emission development strategies, mindful of Article 2 taking into account their common but differentiated responsibilities and respective capabilities, in the light of different national circumstances” (UNFCCC 2015, Article 4.19). This paper aims to explain what are “long-term low greenhouse gas emission development strategies” (LT-LEDS for short), why they are a crucial policy tool, and how countries could go about developing them in order to implement article 4.19. It is important to note that the answers to these questions are not independent: the usefulness of LT-LEDS depends on how they are done.