One of the most efficient tools used in the assessment and diagnosis of childhood anxiety disorders is the self-report questionnaire. The development of self-report questionnaires that reflect the classifications in diagnostic manuals available to clinicians and that are child specific reflects the move within research to advance the understanding of anxiety disorders within children. This dissertation consists of two papers, both of which emphasise the importance of being able to reliably and accurately assess anxiety in children. In order to explore the development of anxiety disorders in children, a literature review covering both adult and child conceptualisations of anxiety, its assessment and treatment was carried out. Given that different anxiety disorders exist within children the i8mportnatc of being able to accurately differentiate and diagnose anxiety disorders is discussed. Early detection and intervention is the key to reducing the impact of anxiety of children's lives, a tool which can be used to screen large numbers of children is required. This basis is used to discuss the clinical, treatment and research implications of self-report questionnaires for childhood anxiety. Suggestions are made as to how these ideas may be taken forward through future research. The empirical paper investigated the psychometric properties and factor structure of the Spence Children's Anxiety Scale as well as producing norms from a community sample of children from the United Kingdom. The clinical and research implications of these findings were discussed.