In recent years, the field of public mental health has received increasing attention in national and international research. However, a key challenge remains to map this field in its interdisciplinarity across the entire spectrum of mental health and lead the discourse between public health, psychiatric epidemiology, mental health promotion, prevention, and health services research in order to realize more fully its innovative potential for improving mental health at the population level. In this interdisciplinary discourse, a number of fundamental conceptual and methodological issues arise, which will be discussed in this essay in relation to Geoffrey Rose's population strategy. In a national initiative across relevant learned societies that has recently been formed, these issues are currently starting to be addressed, also in relation to fundamental causes of social and health inequalities, which ultimately is geared towards more tangible strategies for improving mental health at the population.