In recent years, clinical disorders, including paranoia have been conceptualised as dimensional rather than categorical (Caspi et al., 2013; Ellett et al., 2013). The term 'paranoia' itself has moved into the lexicon of everyday language. Despite this shift, no empirically derived, comprehensive lay definition exists. Two studies are presented that sought to investigate lay conceptions of paranoia in order to develop and validate a prototype of the construct and thereby understand how individuals themselves define and conceptualise paranoia. Study 1 presents a two-part study, aiming to address the question around whether lay views of paranoia have a prototype structure, characterised by a core set of central and peripheral features. Study 1 found evidence that the concept meets criteria for prototypic organisation. The prototype uncovered a view of paranoia that in many ways mirrored that of psychiatric and theoretical conceptions. The second part (Study 2) presents the first steps involved in testing and validating the prototype and was specifically aimed at addressing the question of whether the paranoia prototype is used to guide information processing. Study 2 found, consistent with prediction, that centrality of features affected cognition (Hepper, Ritcher, Sedikides & Wildschut, 2011; Kearns & Fincham, 2004). The prototype was activated to a greater extent when participants encountered a word or phrase that was central to the construct of paranoia. Results from this series of studies provide initial support for the idea that people have and use a prototype for paranoia. The prototype is supportive of dimensional views of paranoia. Despite the need for further validation, the prototype provides an important step in promoting lay views. In addition to this it acknowledges similarities and differences between lay conceptualisations, theoretical and professional perspectives. The thesis concludes with a discussion of theoretical, clinical and research implications of the findings.