Obesity represents a tremendous global health problem. Studies over the past decade have suggested that food addiction (FA), i.e., physical cravings for certain foods - high in fat/sugar - and addiction-like overeating of these types of food, is a likely contributor to the obesity epidemic. While FA has been studied extensively, there are some significant gaps in the literature that need to be addressed:I) Most estimates of the prevalence of FA are based on nonprobability sampling, which significantly limits the representativeness of the prevalence estimates.II) Although addiction disorders are prevalent among individuals with mental disorders, large studies of FA among patients with clinically diagnosed mental disorders are lacking.III) Most addiction disorders are heritable, but the familial transmission of FA remains virtually unknown.IV) Due to a relative lack of longitudinal studies, little is known about the risk factors for and outcomes of FA. To close these gaps in the literature, we designed the Food Addiction Denmark (FADK) project.Methods:The FADK study is a nationwide survey with retrospective and prospective register-based elements. Four randomly sampled cohorts were invited to participate in the survey: 5000 adults and 3750 adolescents from the general population and 5000 adults and 3529 adolescents with a mental disorder. The FADK questionnaire includes the Yale Food Addiction Scale 2.0 and rating scales measuring psychopathology. Data from Danish health and socioeconomic registers will be linked to all invitees.Discussion:We expect that the FADK project will contribute significantly to our understanding of FA.