Genetic diversity is the basis of the ability of organisms to adapt to changes in their environment through natural selection. Populations with little genetic variation are more vulnerable to the arrival of new pests or diseases, pollution, changes in climate and habitat destruction due to human activities or other catastrophic events. The inability to adapt to changing conditions greatly increases the risk of extinction. Genetic conservation and management aimed to save adaptive genetic diversity should be based on the knowledge of the genetic basis of adaptation. The goal of this paper is to describe how adaptive genetic diversity can be measured using new molecular genetic approaches and achievements in forest genomics.