This chapter presents the biology of schizotypal personality disorder (SPD) as model of the interaction of altered brain structure/function and the dopamine system in SPD and schizophrenia. Both schizophrenic and schizotypal patients evince symptoms that are related to psychosis as well as to social deficits. The psychotic symptoms of schizophrenia include hallucinations, delusions, and evidence of gross thought disorder. The psychotic-like or "positive" symptoms of SPD include ideas of reference, magical thinking, perceptual distortions, and possibly suspiciousness. The study of schizophrenia-spectrum personality disorders, particularly SPD, offers a relatively unique opportunity to disentangle and clarify pathophysiological processes that may interact in chronic schizophrenia. Neuropsychological and psychophysiological correlates like poor smooth-pursuit eye movements and poor attentional performance on the Continuous Performance Task (CPT) were particularly associated with "negative" schizotypy. Deficient information processing appears to contribute to the deficit-like symptoms of SPD.