Work-related psychological stress arises when job demands exceed an individual’s resources and capacity to cope. Chronic exposure to stressors leads to psychological and physical strain, and behavioral changes, which adversely impact an individual’s health, motivation, and performance. These impacts extend beyond the individual worker, influencing the functioning of families, organizations, and communities. The costs associated with work-related psychological stress have risen in recent years and are expected to continue rising due to the unprecedented changes and uncertainties brought about by the COVID-19 pandemic, geopolitical tensions, and rapid technological advances. Addressing these challenges requires effective, evidence-based interventions to safeguard employee mental health. This chapter explores key theories of stress and coping, emphasizing contemporary expansions of prominent models. First, an overview of the job demands control (support) theory, conservation of resources theory, job demands resources theory, and the transactional theory of stress and coping is presented. This is followed by a discussion of three key theoretical advancements, including the following: (a) the emergence of positive psychology and the positive impact of good quality work, (b) acknowledgement of broader, socioecological processes in the experience of work-related stress, and (c) the impact of time and reciprocity in the stress process. Finally, the chapter concludes with future directions for theory-driven interventions to provide practical insights and strategies to address the complex and evolving challenges of the modern workplace.