The search for the neural determinants of learning and memory has recently focused on phenomena of neural plasticity. The present paper will try to review and relate the functional significance of such specific plastic changes within neural elements to the process of learning in several species and cell types. Pioneer work proposed in simple organisms and recent emerging evidence on the role of the NMDA receptor complex and calcium-related events will be analyzed in the light of experimental findings suggesting that common biochemical events may underlie different forms of experience-dependent neural adaptation.