This chapter introduces the basic notion of psychosocial occupational health as a concept of growing importance in the world of modern work and employment. Distinct from the traditional focus on material aspects of work environments and their effects on workers’ health, as mainly analysed by occupational medicine and safety sciences, psychosocial work environments address social and psychological aspects that affect workers via sensory input, triggering their cognitions, emotions, motivations, behaviours, and bodily responses. Environmental demands and threats operate at different levels, where most pervasive effects on health are due to distinct adverse exposures at the meso-social level of organizations and enterprises. These exposures are identified with the help of theoretical models, and they are tackled by the workers’ appraisals and coping resources. As work-related health is analysed in a biopsychosocial perspective, different disciplines are engaged in this research. In a further section, the main features of leading disciplines in this field are briefly described: occupational medicine, epidemiology, psychology, sociology, and economics. Cumulative research conducted by these scientific disciplines provides essential knowledge on psychosocial occupational health. The final part of this chapter illustrates the practical relevance of this new knowledge by discussing three major challenges of occupational public health: the COVID-19 pandemic, the widespread prevalence of mental disorders and addictive behaviours in working populations, and the pronounced socioeconomic inequalities in health that persist even in the workforces of economically most advanced societies.