Learning and memory are necessary, fundamental functions that animals need in order to survive and adapt to any environment. The ability to learn and form memory depends on changes occurring in neuronal circuits. These changes occur at both the synaptic level and at the level of changes in intrinsic membrane properties of neurons. Such changes involve physical, structural changes (including growth of new processes as well as retractions of other processes.) Some of these changes may persist throughout the life of the organism while others last for relatively short times. While learning and memory are related, they are separate processes with their own ‘rules and regulations’. Longer lasting memories involve changes in protein synthesis as well as gene activity. The molecular changes that occur in neurons and glia that underlie learning and memory result in structural and biophysical changes in single neurons and neuronal circuits. Some of the chapters in this book present the authors’ findings from specific model systems while other chapters present research concerned with memory consolidation in humans, which can be referred to the process by which the changes in neuronal functioning that occur as a result of learning (i.e. new behavior).