This thesis investigates whether paranormal beliefs are associated with deficits of cognition (in accord with the so-called "cognitive deficits hypothesis"). A systematic review of four decades of research (71 studies, n = 20,993) on paranormal beliefs and cognitive functioning is presented, considering the quality of existing research and identifying areas for future work. It is concluded that study quality in this research area is generally good, although areas of methodological weakness exist including: the lack of preregistration, discussion of limitations, a-priori justification of sample size, and a reliance on undergraduate samples. Heterogeneity of study findings exists, with the most consistent findings emerging for positive associations between paranormal beliefs and both intuitive thinking and confirmatory bias, and a negative association with conditional reasoning ability and the perception of randomness. While most studies suggest a negative relationship between paranormal beliefs and cognitive functioning, the evidence is not convincing of an overall cognitive deficit. The first empirical chapter (Chapter 3) describes the psychometric assessment of the most widely used paranormal beliefs measure, and the subsequent development of a more up-to-date and reliable measure of paranormal beliefs in the general population (owing to issues surrounding the item content and statistical techniques used to develop existing measures). Two methods of scale development (the classical test theory method of factor analysis, and the modern test theory Rasch analysis) were compared, with the Rasch method providing the most prudent measure of paranormal beliefs in the general population. In particular, the Rasch method allowed for assessment of item difficulty, functionality of the rating scale, and differential item functioning. The final scale measures paranormal beliefs along a single dimension using 13 items and a 4-point Likert scale. Chapter 4 seeks to add to the small volume of research concerning paranormal beliefs and executive functions identified in the systematic literature review by examining whether paranormal beliefs are associated with executive difficulties. Specifically, the chapter focuses on cognitive flexibility, presenting a series of replication studies to determine the strength and direction of its association with paranormal beliefs. A negative relationship between paranormal beliefs and cognitive functioning was identified in some studies, however heterogeneity was high between studies and an overall weak effect suggestive of external mediating factors. The final empirical chapter (Chapter 5) explores the subjective importance of personal paranormal experiences for the development and maintenance of paranormal (dis)belief. Compared to sceptics, believers provided more detailed memory descriptions, which were classified into five distinct components representing their paranormal experiences: explaining experiences, intuitions, perceptual experiences, spiritual experiences, and explicit memories of experiences. The memory descriptions of sceptics were shorter and more homogeneous than those of believers and were classified into just two classes: justification of disbelief, and experiences with others. Believers overall emphasised individual experiences, while sceptics focused on shared experiences. Personal paranormal experiences were found to be important for both paranormal belief and disbelief. It is suggested that future research place greater focus on the personal experiences of sceptics, which have received little attention to date, using both qualitative and quantitative methods to better understand paranormal disbelief. While the work presented here identified some cognitive differences between paranormal believers and sceptics, little evidence points to an underlying cognitive deficit associated with paranormal beliefs. This suggests that the cognitive deficits hypothesis present within the literature is not an accurate reflection of the relationship between paranormal beliefs and cognition, prompting the need for a new theory and further investigation. Specifically, the work presented here suggests a new fluid-executive theory to test for a potential difference in fluid intelligence and higher order executive functioning that may influence believers' and sceptics' cognitive performance (particularly on tasks requiring novel or abstract problem-solving). The present work also advocates further research focused on quantitative and qualitative relationships between paranormal disbelief (scepticism) and cognitive functioning; a perspective that has not received adequate investigation in the literature to date.