This systematic review explores the methods and approaches to co-producing digital mental health interventions (DMHIs) and identifies the barriers and facilitators affecting this process. The review included 26 studies across 24 DMHIs, highlighting that co-production with end users is rarely implemented throughout all stages of design, development, and evaluation. Co-production added value by creating culturally sensitive and acceptable interventions, but challenges such as resource constraints, variability in stakeholder suggestions, and power imbalances between stakeholders and researchers were reported. The review found variation in approaches to co-producing DMHIs, with inconsistencies between stakeholder groups, stages of involvement, roles, and methods employed. The review emphasizes the importance of co-production in developing interventions that are more acceptable and engaging for users. Co-production is grounded in self-determination theory, which suggests that involving users in the development process increases their autonomy, competence, and relatedness, leading to better outcomes. Despite this, many DMHIs are publicly available but lack sufficient evidence regarding their design, development, and evaluation. The review also highlights the lack of standardized guidance for involving stakeholders in the design of DMHIs, and the complexity of involving diverse stakeholders such as researchers, service users, health professionals, and app developers. The review outlines various methods used in co-production, including interviews, focus groups, surveys, and prototype testing. It also discusses the roles of stakeholders in the co-production process, ranging from listeners to decision-makers. The review identifies several challenges to co-production, including resource constraints, recruitment challenges, and the need to manage risks such as suicidal ideation. Despite these challenges, co-production is seen as essential for developing DMHIs that are more effective and user-centered. The review concludes that while co-production is increasingly recognized as important, it is not consistently practiced in the development of DMHIs, and there is a need for more standardized guidance and better practices to improve the co-production process.This systematic review explores the methods and approaches to co-producing digital mental health interventions (DMHIs) and identifies the barriers and facilitators affecting this process. The review included 26 studies across 24 DMHIs, highlighting that co-production with end users is rarely implemented throughout all stages of design, development, and evaluation. Co-production added value by creating culturally sensitive and acceptable interventions, but challenges such as resource constraints, variability in stakeholder suggestions, and power imbalances between stakeholders and researchers were reported. The review found variation in approaches to co-producing DMHIs, with inconsistencies between stakeholder groups, stages of involvement, roles, and methods employed. The review emphasizes the importance of co-production in developing interventions that are more acceptable and engaging for users. Co-production is grounded in self-determination theory, which suggests that involving users in the development process increases their autonomy, competence, and relatedness, leading to better outcomes. Despite this, many DMHIs are publicly available but lack sufficient evidence regarding their design, development, and evaluation. The review also highlights the lack of standardized guidance for involving stakeholders in the design of DMHIs, and the complexity of involving diverse stakeholders such as researchers, service users, health professionals, and app developers. The review outlines various methods used in co-production, including interviews, focus groups, surveys, and prototype testing. It also discusses the roles of stakeholders in the co-production process, ranging from listeners to decision-makers. The review identifies several challenges to co-production, including resource constraints, recruitment challenges, and the need to manage risks such as suicidal ideation. Despite these challenges, co-production is seen as essential for developing DMHIs that are more effective and user-centered. The review concludes that while co-production is increasingly recognized as important, it is not consistently practiced in the development of DMHIs, and there is a need for more standardized guidance and better practices to improve the co-production process.