The purpose of the review was to identify and critically analyse the organizational interventions aimed at improving employees’ mental health, in order to detect best practices across organizations and to uncover possible gaps. Through electronic and manual searches, 7,995 articles were initially found. Inclusion criteria were set to select those studies describing interventions conducted in the organizational context and focused on employee mental health. By examining titles, abstracts and full texts, 14 papers were included. These studies covered a variety of interventions and approaches, such as group therapy, work-life balance programs, and manager-level interventions. Additionally, three studies assessed the effectiveness of Employee Assistance Programs (EAPs) aimed at enhancing individuals’ mental health via counselling. Overall, two different intervention types emerged, namely individual-level interventions, focusing on the single employee, and organizational-level interventions, targeting organizational or work conditions. The interventions are described in details and, drawing upon the realist evaluation approach, the mechanisms responsible for their success (or failure) are identified. The main mechanisms pertain to changes in employee cognitive models, job attitudes or lifestyle habits, modifications in working conditions, and the active involvement and participation of employees and management in the intervention. Best practices for the design of future initiatives are offered, and some of the main limitations and gaps in the literature are discussed, such as the predominant focus on the results of the intervention rather than on the process, and the prevalence of short-term individualistic approaches that minimizing the role of organizations in creating or exacerbating employees’ mental health conditions.