Defining Erectile Dysfunction is complex, and despite its prevalence, costs, and implications for quality of life, it is not well-characterised epidemiologically. Psychogenic factors are involved alone or in combination with organic causes in many cases, but scientific research is sparse and Psychogenic Erectile Dysfunction is usually diagnosed by excluding organic causes. This book reviews the relevant scientific literature and introduces the findings of a recent clinical cross-sectional study examining specific sexual behaviours, cognitions, and emotions during masturbation and partner sex, in men with and without Erectile Dysfunction, in order to identify those factors which distinguish men with Psychogenic Erectile Dysfunction from those men without this condition. Importantly, findings failed to support the traditional use of REM sleep and masturbatory erections to differentiate between Organic and Psychogenic Erectile Dysfunction. A complex relationship between cognitions, emotions and sexual behaviour in men with Psychogenic Erectile Dysfunction is suggested. This study is of interest to psychosexual therapists, clinicians, and those involved in sexual research.