Background <p>Depression is a common mental disorder that has a profound impact on daily life and increases the risk of chronic diseases and mortality. Adherence to treatment guidelines would produce better patient outcomes but is often suboptimal. The objective of this systematic review was to examine adherence to evidence-based treatment guidelines for depression, identify factors that influence adherence and understand how to improve it.</p> Methods <p>We searched the PubMed, Web of Science and Cochrane databases. We included original trials, studies dealing with treatment-related guidelines and patients suffering from depressive disorders. We excluded reviews, study protocols and studies that dealt exclusively with mental disorders other than depression.</p> Results <p>85 studies met the inclusion criteria. Six studies focused on young subjects, three on the perinatal population and three on the elderly. A few studies concerned a population with somatic (<i>n</i> = 11) or psychiatric (<i>n</i> = 25) comorbidities. Eight articles focused on ethnic minorities.</p> Discussion <p>The lack of standard measurement on adherence and the variability in adherence rates highlight the complexity of assessing and implementing guideline-concordant care, and the associated challenges.&#xa0;Factors that influence adherence, such as those related to patients and their comorbidities, physicians, and guideline-related factors, play a significant role in determining whether appropriate treatment is received.&#xa0;Despite the complexity and cost of these strategies, multifaceted approach to guideline implementation, including the active involvement of clinicians, ongoing monitoring, and organisational support, improves guideline adherence.</p> Conclusion <p>This review provides a comprehensive overview of the current state of guideline adherence in treatment of depression and identifies areas for quality improvement initiatives.</p>