The volume “Essential Concepts for Implementing the Sustainable Development Goals: An A-Z Guide” (Routledge 2025), edited by Frank Biermann, Thomas Hickmann, Yi hyun Kang, Carole-Anne Sénit and Yixian Sun, offers an overview of key aspects and terms for implementing the Sustainable Development Goals (SDGs). In her contribution on the “Planetary Boundaries”, Prof. Dr. Lena Partzsch explains the framework, which was published in 2009 and has since been revised and expanded several times. It identifies nine interconnected processes that are crucial for maintaining the stability and resilience of the entire Earth system. Six of the nine boundaries have now been transgressed: Climate change, biosphere integrity (genetic diversity), biogeochemical fluxes (nitrogen and phosphorus), land system change, freshwater use, and chemical pollution. Ocean acidification is close to the tipping point, while aerosol deposition is regionally exceeding the tipping point. Stratospheric ozone levels have recovered slightly. Despite criticisms, including that it neglects historical and regional heterogeneity, the framework proved to be an effective communication tool. It has ensured that the alarm has been sounded in the scientific and political debates about the postponement and non-implementation of the environmental targets in the SDGs.