This chapter defines afforestation/reforestation (AR) and provides insights into its role and value for achieving negative emissions. It contains a synthesis of the current research knowledge and gaps in the most up-to-date literature on AR, and a complete analysis of AR including forest growth, biogenic carbon sequestration, risk-adjusted carbon sequestration and forestry operations. More specifically, GHG balance, cost and water footprint analyses are carried out at the sub-regional level in five archetypal regions (Brazil, China, European Union, India and United States) over a 200-year time-period.