Background In recent years, internet- and mobile-based interventions (IMIs) have become increasingly relevant in mental health care and have sparked societal debates. Psychotherapists’ perspectives are essential for identifying potential opportunities for improvement, facilitating conditions, and barriers to the implementation of these interventions. Objective This study aims to explore psychotherapists’ perspectives on opportunities for improvement, facilitating conditions, and barriers to using IMIs. Methods The study used a qualitative research design, utilizing open-ended items in a cross-sectional survey. A total of 350 psychotherapists were asked to provide their written opinions on various aspects of IMIs. Thematic analysis was conducted to analyze the data and identify core themes. Results The analysis revealed 11 core themes related to the use of IMIs, which were categorized into 4 superordinate categories: “Applicability,” “Treatment Resources,” “Technology,” and “Perceived Risks and Barriers.” While many psychotherapists viewed IMIs as a valuable support for conventional psychotherapy, they expressed skepticism about using IMIs as a substitute. Several factors were perceived as hindrances to the applicability of IMIs in clinical practice, including technological issues, subjective concerns about potential data protection risks, a lack of individualization due to the manualized nature of most IMIs, and the high time and financial costs for both psychotherapists and patients. They expressed a desire for easily accessible information on evidence and programs to reduce the time and effort required for training and advocated for this information to be integrated into the conceptualization of new IMIs. Conclusions The findings of this study emphasize the importance of considering psychotherapists’ attitudes in the development, evaluation, and implementation of IMIs. This study revealed that psychotherapists recognized both the opportunities and risks associated with the use of IMIs, with most agreeing that IMIs serve as a tool to support traditional psychotherapy rather than as a substitute for it. Furthermore, it is essential to involve psychotherapists in discussions about IMIs specifically, as well as in the development of new methodologies in psychotherapy more broadly. Overall, this study can advance the use of IMIs in mental health care and contribute to the ongoing societal debate surrounding these interventions.