Smartphone applications ("apps") may contribute to closing the treatment gap for depression by reaching large populations at relatively low costs. The general public seems open towards the use of apps for mental disorders but less is known about the attitudes of health care professionals. Therefore, the aim of this study was to examine the available evidence on the effectiveness of apps for depression and to explore the attitudes of health care professionals towards their use in practice. A systematic literature search was performed aimed at studies utilizing smartphone applications for depression. In addition, a survey was conducted to explore health care professionals' attitudes towards using these treatment apps in clinical practice. Twelve articles were identified in the systematic literature review. All included trials reported a decline in depressive symptoms after the intervention periods. In the survey, 72 health care professionals participated. Significant differences were found between the level of technology experience and how much the health care professional would consider the use of mobile applications in clinical practice. Survey participants reported openness towards therapeutic app use but very little knowledge and experience in the field. Apps appear to be a promising self-management tool for reducing depressive symptoms. Despite some concerns, health care professionals' attitudes towards the use of smartphone applications in clinical practice are quite positive. The provision of information on the potential benefits of e-health interventions as well as the training of professionals in the application of new technologies may increase health care professionals' awareness and knowledge about mobile apps for the treatment of mental disorders.