Decarbonization and defossilization are two complementary strategies addressing climate change while recognizing carbon’s irreplaceable role in life and industry. Carbon cannot be removed from human society: it forms the basis of all organic life, pharmaceuticals, plastics, steel, and advanced materials like graphene. Its unique chemical properties enable complex molecules essential for biology, medicine, and technology. Decarbonization primarily targets the reduction of CO₂ emissions to achieve net-zero, focusing on energy systems, transportation, and heavy industry. It involves shifting from fossil fuels to renewables, electrification, and carbon capture and storage (CCS), allowing residual emissions to be offset. This approach successfully cuts direct greenhouse gas releases but does not address sectors where carbon is a structural necessity rather than just an energy source. Defossilization specifically tackles dependence on fossil-derived carbon feedstocks, replacing them with sustainable alternatives in industries like chemicals and materials. It sources renewable carbon from three main pathways: biomass (plants, algae, waste), captured CO₂ (via CCU), and recycling (mechanical or chemical). These methods maintain carbon’s utility—producing plastics, fuels, and chemicals—while closing the carbon loop, avoiding new fossil extraction and enabling circularity. Together, the strategies form a holistic framework: decarbonization eliminates emissions from energy use, while defossilization secures sustainable carbon supply for non-energy applications. Challenges include higher costs, land-use conflicts for biomass, and scaling CCU technologies. However, innovations in bio-based materials, microbial synthesis, and CO₂ utilization are advancing both goals. Ultimately, the transition redefines carbon from a climate liability to a managed resource, supporting economic continuity alongside environmental protection.