This new clinical practice guideline concerns the psychosocial diagnosis and treatment of patients before and after organ transplantation. Its objective is to establish standards and to issue evidence-based recommendations that will help to optimize decision making in psychosocial diagnosis and treatment. For each key question, the literature was systematically searched in at least two databases (Medline, Ovid, Cochrane Library, and CENTRAL). The end date of each search was between August 2018 and November 2019, depending on the question. The literature search was also updated to capture recent publications, by using a selective approach. Lack of adherence to immunosuppressant drugs can be expected in 25-30% of patients and increases the odds of organ loss after kidney transplantation (odds ratio 7.1). Psychosocial interventions can significantly improve adherence. Metaanalyses have shown that adherence was achieved 10-20% more frequently in the intervention group than in the control group. 13-40% of patients suffer from depression after transplantation; mortality in this group is 65% higher. The guideline group therefore recommends that experts in psychosomatic medicine, psychiatry, and psychology (mental health professionals) should be involved in patient care throughout the transplantation process. The care of patients before and after organ transplantation should be multidisciplinary. Nonadherence rates and comorbid mental disorders are common and associated with poorer outcomes after transplantation. Interventions to improve adherence are effective, although the pertinent studies display marked heterogeneity and a high risk of bias.