Obsessive-compulsive disorder (OCD) is characterized by recurrent unwanted intrusive thoughts that evoke enormous distress and contribute to functional impairment. Cognitive theories of OCD posit that appraisals about the significance of thoughts are critical in the development and persistence of obsessions. In his theory; Rachman (1997) suggests that appraisals of unwanted thoughts distinguish clinical obsessions from normal intrusive thoughts; thoughts appraised as important and personally significant will be upsetting and recur. Moreover, cognitive theories propose that appraisals motivate thought suppression, which results in a paradoxical increase in the frequency of thoughts. This dissertation project was designed to examine several key tenets of Rachman's (1997) cognitive theory of obsessions. First, if appraisals of unwanted intrusive thoughts are relevant to OCD, a positive relationship should exist between appraisals and OCD symptomatology. To explore this hypothesis, nonclinical participants in Studies 1 and 2 read four vignettes, each portraying a prototypical obsession of aggressive, sexual, blasphemous, and racist themes, and indicated their appraisals about the personal significance of the intrusive thoughts. Questionnaires assessing obsessive-compulsive (OC) symptoms, OC beliefs, and depression were also administered. Results revealed that appraisals of the intrusive thoughts were related to subclinical OC symptoms and OC beliefs. Moreover, there was evidence that appraisals varied according to thought content and thought frequency. Second, the cognitive theory of obsessions implicates thought suppression in the development and persistence of obsessions. The purpose of Study 3 was to investigate whether the effects of thought suppression would differ depending on the personal meaning of the target thought. Sixty high religious and 60 low religious participants were randomly assigned to suppress or not suppress a blasphemous target thought. Number of thought recurrences, thought control effort, anxiety, and mood were assessed. Results revealed that appraisals of personal meaning, when combined with thought control effort, were associated with negative mood and increased anxiety. There was also partial support that thought suppression had differential effects on target thought frequency according to the personal meaning of the target thought. The implications of this research are discussed with a focus on the proposed role of appraisals in the development of intrusive thoughts.