This paper attempts to indicate which aspects of mental well-being of employees have already been discovered and described using the scientific method, and which remain unknown. The article provides the definitions of mental well-being, based on various thinking systems, as well as cases explaining the concept of employee well-being. In research on well-being, we deal with three research orientations, i.e., the hedonistic approach (subjective) and the eudaimonistic approach (objective), as well as the school integrating both approaches. Several results of research on the correlation between the well-being of employees and other variables in the organization were also presented: the influence of the work environment, human resource management practices, the use of corporate social media, and the influence of the company's specific organizational culture. The article also includes statistical data and examples of understanding well-being in management practice. A particularly important aspect raised in the article was the construction of questions related to the well-being of employees, precisely in the context of management practice, and the preparation of practical recommendations. Possible directions for further research were also indicated, especially on the basis of the aspects cited in the article.