Memory, the ability to store and retrieve information, is essential for learning in children. Modern neurobiology research is revealing some of the fundamental steps that encode memories within networks of neuronal synaptic connections in the brain. Somewhat different networks store verbal declarative memories and habit or procedural memories. Several biochemical steps convert short-term memories into permanent memories. These changes include activation of neurotransmitter and growth factor receptors, intracellular protein kinases, and nuclear transcription factors that stimulate gene expression of memory proteins. The proteins strengthen synaptic connections and stabilize long-term memories. Genetic defects in those pathways appear to be responsible for several human retardation and learning disability syndromes, including Coffin-Lowry syndrome and neurofibromatosis.