Background: Although shared decision making has been widely advocated in mental health policies in western countries, there is limited evidence of shared decision making in South Asian cultures, particularly Taiwan. Thus, there is a need to explore shared decision making from the perspectives of Taiwanese health professionals and individuals experiencing mental health disorders. Such knowledge is of key importance to facilitate shared decision making in Taiwan's mental healthcare systems. Aims: To explore/understand the process of decision making, from both health professional and patient perspectives, in secondary mental healthcare in Taiwan. Methods: To address this aim, three separate but interrelated studies were conducted: *Study One: A systematic review of previously published qualitative studies of patient perspectives of shared decision making. *Study Two: Semi-structured qualitative interviews to explore patient perspectives of shared decision making in secondary mental healthcare in Taiwan. *Study Three: Semi-structured qualitative interviews to explore health professional perspectives of shared decision making in secondary mental healthcare in Taiwan. Results: *The qualitative systematic review included 13 studies, and revealed a number of key barriers and facilitators to shared decision making. Barriers included: paternalistic attitudes of health professionals, poor quality interaction with health professionals, and lack of professional knowledge and information. Factors enhancing shared decision making included a supportive attitude to patient involvement, sufficient information exchange, and other support resources. *Qualitative interviews with 20 patients found that they were not involved in the decision-making process due to: the professional status of health professionals in a submissive culture; negative perception of making decisions; and health professionals having limited time. However, patients showed a desire to be involved in decision making but required sufficient information exchange to enable them to do this. *Qualitative interviews with 24 health professionals revealed a number of barriers to and facilitators of shared decision making. Factors reducing shared decision making included: the powerful status of health professionals and families; a belief that patients had impaired decisional ability due to their mental illness; a lack of understanding of shared decision making; and insufficient time. Despite this, there was a view from a few health professionals that they understood the potential benefits of shared decision making. The results of the above three studies were synthesised and revealed three mechanisms through which implementation of shared decision making could potentially be improved: capability/skill improvement; attitude/motivation modification; and sufficient time resource. Conclusion: This study has provided an insight into implementing shared decision making in mental healthcare directly from patients' and health professionals' perspectives in Taiwan. The findings revealed that shared decision making was not yet understood or implemented in mental healthcare. Significant barriers and facilitators were identified and mechanisms were proposed to address the barriers to shared decision making. The findings of this study provided potential solutions to aid further training of staff and development of national policies on shared decision making.