Qualitative diary methods (QDMs) have great potential for mental health research, as they provide rich data about experiences and phenomena as and when they happen, from the perspectives of participants themselves. They provide unique insight into behavior, cognitions, and change over time in greater depth and detail than other quantitative or qualitative methods might offer. This paper presents the results of a scoping review of QDMs in mental health research, aimed at clarifying how diary methods are used in mental health research, and outlining key decisions and considerations in planning and conducting a qualitative diary study. Forty-eight papers were reviewed, and the findings highlight different elements of QDMs. The research aims, suitability for participants, and ethical issues are first discussed, followed by elements of diary study design including diary format, administration, intervals, timeline, sample size, diary structure and guidance, and additional data collection methods. Finally, analysis approaches and the strengths and challenges of QDMs are reviewed. Discussion around the future of QDMs follows, including a checklist for conducting and reporting a qualitative diary study.
