As the aging of the productive age population is accelerating, the health of workers has recently been drawing more attention. In this article, from the view point of labor economics, we summarize and provide an overview of what has been clarified about the relationship between work and mental health from previous studies, with a wide range of readers in mind. Research related to work and health can be roughly divided into two viewpoints; one to verify the effect of work on health and the other to assess the effect of health on work (productivity). In this paper, we first review and discuss previous studies on the health effects of work. Specifically, we will show several estimation results based on the econometrics to see how the length of working hours, work style, and the relationship with bosses could affect the health of individual workers. We then look at studies that focus on firm-level productivity to confirm that workers' mental health affects firm productivity. Specifically, it will be shown that the deterioration of workers' mental health could adversely affect the firm's performance together with subjective indicators of the productivity of individual workers. Finally, based on what has been revealed in previous studies, we will examine how necessary policies and measures should be taken. We argue that the intervention by a third party such as a government or a firm is necessary. We discuss how the roles of firms are important, especially in Japan, and emphasize that health measures and work style reform taken by firms are effective for improving workers' health.