This chapter reviews empirical findings from a prospective, longitudinal study of offspring of schizophrenic parents. Specifically, it focuses on a series of taxometric analyses that attempt to discern whether schizotypal symptoms and signs assessed during childhood, young adulthood, and middle age define a latent class of individuals with high risk for developing schizophrenia-spectrum disorders, and examines the stability of schizotypal class membership across the life-span. The chapter reviews the genetic relationship between schizophrenia and schizotypal personality disorder (SPD) and the contributions of environmental factors to the development of schizophrenia in genetically at-risk individuals. It also explains premorbid behavioral antecedents of the schizophrenia spectrum and stability of schizotypal symptoms and signs over time. The chapter explains taxometric analyses of putative schizotypy indicators from the Copenhagen schizophrenia high-risk project. It concludes with evidence that the signs and symptoms of SPD define a class of individuals with high risk for schizophrenia-spectrum disorders.