Psychiatric epidemiology constitutes an important subdiscipline of scientific psychiatry. Nevertheless, it still lags behind other branches of epidemiology. This has been attributed to the difficulties encountered in conceptualising and measuring mental disorders.1 It is only recently that the emphasis in the field has shifted from descriptive to analytical research and this is probably because of the influences from genetic epidemiology and social sciences.2 Psychiatric epidemiology has taken most of its tools from general epidemiology—that is, chronic disease epidemiology.3 It is therefore not surprising that no fundamental differences between the mother discipline and her psychiatric descendant exist. Yet, there are particular challenges in the conduct of psychiatric epidemiological research that are absent or less prominent in general, mostly somatically oriented, epidemiology.4 Challenges particularly encountered in psychiatric epidemiology include 1. Assessment of caseness: psychiatric diagnoses are mostly made on the basis of symptoms—patients’ reports of their subjective experiences—and not signs, like fever in general medicine. Moreover, there are no pathognomonic symptoms or signs; 2. Neither most mental disorders nor their best-known risk factors, like social deprivation, stress exposure, lack of social support, social isolation, abnormal personality traits or genetic liability, are as easily captured in a singular variable as tends to be the case in the epidemiology of somatic disease; 3. Making a psychiatric diagnosis is costly in time and effort; and 4. Information bias and non-response bias are more of a problem in psychiatric epidemiology than in other branches of epidemiology. In our view, this warrants recognition of the epidemiology subspecialty “psychiatric epidemiology”. In trying to cope with the above-mentioned challenges, psychiatric epidemiology has developed a set of concepts, albeit limited, and vocabulary of its own. The purpose of this glossary is to provide brief definitions, sometimes with comments, of frequently used special terms one may come across in dealing with …