Modulation of local protein synthesis in neuronal dendrites plays a key role in the production of long-term, activity-dependent changes in synapse structure and functional efficacy. Such long-term changes also require regulation of actin dynamics in dendritic spines. Recent evidence couples local protein synthesis to regulation of actin dynamics in long-term synaptic plasticity. Translation of the dendritically localized mRNA, Arc, is required for consolidation of LTP and stabilization of nascent polymerized actin. BDNF signaling activates Arc-dependent LTP consolidation and is required for actin polymerization and stable expansion of dendritic spines during LTP. Regulation of actin pools within dendritic spines modulates spine size and enlargement, organization of the postsynaptic density, receptor trafficking, and localization of the translational machinery.