Biochar systems for carbon storage in soils: Biochar is the product of thermochemical conversion of biomass under reduced oxygen supply. Ancient people of Amazonia created fertile and soil organic matter-rich Anthrosols such as the famous Terra Preta by incorporating charring residues together with nutrient-rich kitchen midden and excrements in a region, which is dominated by highly weathered and nutrient-poor tropical soils. Using biochar to increase and stabilize soil carbon stocks is a promising strategy for tackling the climate crisis, which is why modern research is trying to adapt this first and famous Terra Preta biochar system and bring it into the modern era. The objective of this chapter is to summarize the current state of research on this negative emission technology, to provide an overview of various field-tested modern biochar systems, and to outline the limitations of biochar technologies.