Williams syndrome is a neurodevelopmental disorder that results from the deletion of ~25-30 genes spanning about 1.5 megabases in the q11.23 region of chromosome 7. Patients with this syndrome present with a combination of a distinctive elfin-like facial appearance; growth retardation; mild mental retardation; an inconsistent cognitive profile that includes visuospatial impairments with good facial discrimination and relatively preserved expressive language skills; and cardiovascular abnormalities. In addition, a striking behavioral feature of the syndrome is the high sociability and empathy that these patients show for others. The study of patients with “partial” deletions of the chromosome band 7q11.23, mutated genes in this region and knockout mice with deletions of specific genes in the homologous G1–G2 region of mouse chromosome 5 are clarifying some genotype/phenotype relationships. Futhermore, genes located in this region that are prominently expressed have been implicated in brain development and function.The neuropsychological profile of patients with Williams syndrome is heterogeneous, highlights important dissociations between cognitive functions and suggests that the behavioral dimensions of sociability, empathy, engageability, and talkativeness may be independent of, or not easily explained by, the cognitive deficits. Williams syndrome has enormous heuristic value because its pathological feature of heightened “sociability” can be a “deficit” symptom of major complex neuropsychiatrie disorders, such as schizophrenia and autism. Data consistent with a core inability of patients with Williams syndrome to inhibit social approach suggest that this disorder may afford an opportunity to study the biological basis of the “drive” toward socialization. From a research perspective, the syndrome lends itself to neurobiological studies of sociability as a dimension that varies independently of cognition (or at least many separable cognitive processes). Importantly, from a clinical perspective, the syndrome challenges us to administer strategic psychosocial interventions that take advantage of the opportunities that “pathological” sociability provide, while avoiding its threats. An illustrative example of an effective strategically planned psychosocial intervention for a patient with Williams syndrome is briefly presented.