Although current guidelines recommend collaborative care for severely depressed patients, few patients get adequate treatment. In this study we aimed to identify the thresholds for interdisciplinary collaboration amongst practitioners when treating severely depressed patients. In addition, we aimed to identify specific and feasible steps that may add to improved collaboration amongst first and second level Belgian health care providers when treating depressed patients. In two standard focus groups (n = 8; n = 12), general practitioners and psychiatrists first outlined current practice and its shortcomings. In a next phase, the same participants were gathered in nominal groups to identify and prioritise steps that could give rise to improved collaboration. Thematic analyses were performed. Though some barriers for interdisciplinary collaboration may seem easy to overcome, participants stressed the importance of certain boundary conditions on a macro- (e.g., financing of care, secure communication technology) and meso-level (e.g., support for first level practitioner). Findings are discussed against the background of frameworks on collaboration in healthcare and recent developments in mental health care.