Epidemiology explores the distribution and key factors of an illness or other health-related situations so as to apply those findings to the management and treatment of the illness. In that sense, it is an essential framework for identifying healthcare policy and service provision priorities and is also a vehicle that helps to design effective and feasible prevention interventions. From that perspective, it is – in some way – in the service of public health. While drawing conclusions and extrapolate findings to the population from the sample, epidemiologists frequently take into account the role of chance, bias, confounding and the direction of causality on the association observed between the exposure and the outcome/illness. Depending on the research questions posed and the availability of materials and human resources, they select epidemiological designs that will make it easier to achieve the goals of a study. The main research designs are ecological studies, cross-sectional studies, case control studies, longitudinal cohort studies and randomised controlled trials. They also make every effort to minimise the occurrence of bias and to control for confounding. Despite the importance of epidemiology worldwide with regard to its contribution to evidence-based medicine and the provision of quality services, Greece has failed to establish an epidemiology-based psychiatry culture. Nationwide studies are scarce, and links between epidemiological findings and mental health policies have not been made. To date, policies appear to be based on intuition, extreme empiricism, sloppy approaches, the "guild mentality", political interests or individual beliefs; and while there may be some examples of best practice in terms of the services provided, overall services are not imbued with and integrated into a central, national strategic plan for mental health. Under pressure from the global mental health movement, the development of psychiatric epidemiology in Greece is not only a vital necessity but also a major challenge.