Dendritic spines are small bulbous protrusions on the surface of dendrites that serve as principle postsynaptic targets for excitatory synapses (1-3). Structural modifications of dendritic spines have been implicated as a cellular basis for learning and memory. Morphological abnormalities of spines are observed in some neurological diseases such as mental retardation and schizophrenia (4). Thus, studies on the morphological regulation of dendritic spines could have strong relevance to our understanding of the molecular mechanisms of the higher brain function and the pathophysiology of neurological disorders. Here we review recent progress on the role of the cell surface heparan sulfate proteoglycan syndecan-2 and ephrin-Eph signaling in dendritic spine development. Information from these new developments suggests a model in which cell surface ephrin-Eph signaling induces clustering of syndecan-2 and recruitment of cytoplasmic molecules, which leads to localized actin polymerization via Rho family GTPases, N-WASP, and the Arp2/3 complex.