Chemical substances make up the world around us, including ourselves. Whether we are frying food, fertilising soil, or simply breathing, we are actors in a chemical world, changing chemical environments on micro- and macro-scales. Industrialisation, and particularly the large-scale production of chemicals, has brought about new ways in which chemicals affect human health, ecosystems and the global climate. Increasingly, chemists grapple with this responsibility and seek to establish sustainable or ‘green’ chemical practices. This requires an understanding of the role of chemicals in open systems that transcend disciplines, scales, and levels of complexity. The proposed project seeks to articulate the philosophical foundations of sustainable chemistry. It explores three key themes: the causal relationships of chemical substances across molecular, ecological, and global scales; the role of evidence and inference in understanding these complex causal networks; and the concept of chemical hazards, considering both individual substances and broader systemic risks. Thus, the project not only advances the philosophy of chemistry but provides a much-needed contribution to sustainability discussions within chemistry.