Soil carbon sequestration (SCS) is a critical natural process through which atmospheric carbon dioxide (CO?) is captured by vegetation and stored in soil organic matter. With global soils estimated to hold between 1,500 and 2,400 petagrams of carbon, they represent the Earth's largest terrestrial carbon reservoir. This article reviews the key mechanisms of SCS? including microbial processing, organo-mineral interactions, and physical protection within soil aggregates?and examines how these processes operate across forest, grassland, and wetland ecosystems. The threats posed by land-use change and climate warming, as well as management strategies to enhance soil carbon storage, are also discussed. Understanding and harnessing SCS is essential for achieving global climate change mitigation targets.