Climate change has been partially mitigated by an increasing net land carbon sink in the terrestrial biosphere; understanding the processes that drive the land carbon sink is thus essential for protecting, managing, and projecting this important ecosystem service. In this Review, we examine evidence for an enhanced land carbon sink and attribute the observed response to drivers and processes. The land carbon sink has doubled from 1.2 ± 0.5 PgC yr-1 in the 1960s to 3.1 ± 0.6 PgC yr-1 in the 2010s. This trend results largely from carbon dioxide (CO2) fertilization increasing photosynthesis (driving an increase in the annual land carbon sink of >2PgC globally since 1900), mainly in tropical forest regions, and elevated temperatures reducing cold-limitation, mainly at higher latitudes. Continued long term land carbon sequestration is possible through the end of this century under multiple emissions scenarios, especially if nature-based climate solutions and appropriate ecosystem management are deployed. A new generation of globally distributed field experiments are needed to improve understanding of future carbon sink potential by measuring belowground carbon release, the response to CO2 enrichment, and long-term shifts in carbon allocation and turnover .