This book integrates discoveries from recent years to show the diversity of molecular mechanisms that contribute to memory consolidation, reconsolidation, extinction, and forgetting. It provides a special focus on the processes that govern functional and structural plasticity of dendritic spines. In nine chapters, new and important ideas related to learning and memory processes will be presented. Themes discussed include the role of AMPA receptors in memory, two signalling cascades involved in local spine remodelling and memory, the role of extracellular matrix proteins in memory, the regulation of gene expression and protein translation, and mechanisms of retrieval-induced memory modulation and forgetting. We believe that the study of these topics represents a great step toward understanding the complexity of the brain and the processes it governs.