Despite a standard classification and array of self-report questionnaires, there is little consensus about how to define and measure sexual dysfunction. Recently the debate has been influenced by the pharmaceutical industry, leading to an increasingly medicalised view of sexual difficulties. The aim of this thesis was to explore the meaning of sexual (dys)function to those who have and have not experienced sexual difficulties; and to use these meanings to create a conceptual model and population prevalence measure of sexual dysfunction for use in UK community surveys. Thirty-two semi-structured interviews were conducted with individuals recruited from a GP practice, an HIV/AIDS Charity and a Sexual Problems Clinic. The data were analysed using principles derived from Grounded Theory. Variation in individual meaning was expressed in terms of three distinct versions of functional sex - the erotic, the interpersonal and the mechanistic - which framed the purpose of sexual activity, the criteria determining ideal sex, and threats to this ideal. The data highlighted several coping strategies that individuals adopted when their lived reality failed to match their ideal: changing circumstances to fit goals, for instance by seeking a medical cure; changing goals to fit circumstances, for instance by lowering expectations; And living with the gap between ideal and actual experience, for instance by avoiding the problem. Choice of strategy and the likelihood of successful adjustment were influenced by the severity of the problem, causal attributions made about the problem, and the partnership context. Thirty-one potential components of a functioning sex life were identified from the data. Using evidence both from the literature and from this study, 12 of these components were selected for inclusion in a conceptual model of sexual function. This model was transformed into a 19-item draft prevalence measure of sexual dysfunction ready for psychometric testing and validation.