Science, society, and mental retardation: a history -- Neurogenesis, neuronal migration, maturation, and function: insights into learning and memory -- Structural brain anomalies and neural tube defects -- Mental retardation associated with dysmorphology, growth retardation, or overgrowth -- Mental retardation associated with other neurological defects -- Mental retardation that develops after a period of normal cognition -- Non-syndromic mental retardation, autism, and language deficits -- Genomics, functional genomics, and epigenetics -- Establishing a diagnosis and determining etiology -- The value of genetic diagnosis: applying knowledge about etiology to prevention and treatment -- Epilogue: The value of genetic diagnosis--Applying knowledge about etiology to prevention and treatment.