The ecological transition – and more particularly the climate transition, which is an essential component – is one of the major challenges of the 21st century. One of the first urgent needs of this transition is to reduce greenhouse gas (GHG) emissions in order to limit the importance of the additional greenhouse effect and the impacts of induced climate change, which endanger the habitability of our planet and the survival of living species. The COP21 decided to limit the temperature increase to 1.5°C by 2050 instead of 2.5°C. COP26 confirmed and emphasized this objective, which is currently non reachable if the situation remains unchanged, according to many experts. Carbon neutrality on a global scale and by 2050 remains the most viable alternative in order to reach this objective. It must be implemented at the regional, national and local levels and translated into actions to reduce emissions and increase storage and sequestration capacities. It appears necessary for territories to have relevant measurement methods and indicators to enable them to monitor their carbon trajectory and their contribution to the collective objective of carbon neutrality. These tools help to establish the climate diagnosis of the territories and are the first step to set realistic objectives, implement coherent strategies and identify concrete solutions to be deployed. This would maximize their chances of achieving their ambitions. Finally, these tools would allow to ensure the management and the evaluation of the actions undertaken.