Neurogenesis, the generation of new neurons from neural precursor cells (NPCs), is a multi-step process that includes the proliferation of NPCs, fate determination, migration, and neuronal maturation. Neurogenesis is regulated by several extrinsic factors, such as enriched environment, physical exercise, hormones and stress, many of which also induce the expression of neurotrophins. In this review, we summarize studies on the role of neurotrophins in neurogenesis during development and in adults. We discuss the functional significance of neurogenesis in learning and memory, and how neurotrophins regulate this process. In this context, we describe recent experiments linking adult neurogenesis to long-term synaptic plasticity in the hippocampal dentate gyrus. Further study of the relationship between neurotrophins, adult neurogenesis and dentate synaptic plasticity might provide new insights into the mechanisms by which gene–environment interactions control cognition and brain plasticity.