Traditional cognitive-behavioural treatment of eating disorders has focused on factors that maintain the disorders. These treatments have achieved some success with individuals with bulimia nervosa (BN), but there is no evidence- based treatment for anorexia nervosa (AN) and eating disorder not otherwise specified (EDNOS). Researchers are starting to explore the role of core beliefs in the development and maintenance of eating disorders, with the hope that broader models can be developed that will enable us to treat them better. The first paper presents a systematic review of the literature regarding the relationship between core beliefs and eating disorders. It focuses on studies that have used the Young Schema Questionnaire (YSQ) to measure core beliefs in people with eating disorders. Twenty-two studies' findings are discussed and critiqued. Few consistent patterns have emerged regarding the association between core beliefs and eating disorders, and more work is needed in increasing studies' methodological rigour and exploring the effectiveness of core belief measures developed specifically for eating disorders. The second paper investigates the relative usefulness of the YSQ and the recently developed Eating Disorder Core Belief Questionnaire (ED-CBQ) in predicting eating disorder symptoms in participants with AN, BN and EDNOS (213 participants in total). It also explores whether the diagnostic groups differ in their core beliefs. Results indicate that the ED-CBQ may be more useful than the YSQ with this population at predicting eating disorder symptoms. In addition, there appear to be some differences in anorexic-type (AN and EDNOS-AN) and bulimic-type (BN and EDNOS-BN) participants in their core beliefs, and a few differences in AN and BN participants as well. Further research is needed with larger numbers to verify the results. However, the study confirms the importance of core beliefs in eating disorders and a need to consider them during treatment.