This book reviews the dimensional conceptualization of persecutory delusion in the attempt to elucidate the transition from suspicious thinking to clinically relevant paranoia. A better understanding of psychosis may take advantage from the study of non-clinical population; to this aim this book's chapters review recent research work and theoretical framework used for interpretation. Current epidemiological investigations on psychotic features in the general population are summarized, and the findings are framed using the dimensional and quasi-dimensional models of psychotic symptoms distribution. Finally, the concept of paranoia as a general cognitive process, in the form of heuristic, is proposed to reconcile experimental and epidemiological findings.