Carbon is a vital element in the biosphere due to its abundance in living organisms. It exists in both pure and chemically bound forms and has the capacity to form a wide range of complex compounds, making it integral to industrial society. Since the Industrial Revolution, carbon-based fuels (e.g., coal, oil, natural gas) have been the primary sources of energy, but their combustion releases CO2, contributing significantly to anthropogenic climate change. Despite the need to limit fossil fuels, hydrocarbons will remain crucial for sectors like chemicals and transportation, where alternative energy sources are challenging to implement. Sustainable synthetic or biologically produced hydrocarbons may offer alternatives for hard-to-decarbonize sectors. This chapter examines carbon availability, focusing on CO2 provision options, categorizes carbon sources (fossil, biogenic, mixed), and assesses their potential in transitioning toward a defossilised energy and economic system.