Qualitative single case studies offer insights into developmental processes within specific contexts. Case studies enables us to investigate how development takes place, since it allows for a detailed examination of therapeutic processes, relationship dynamics, and developmental trajectories. Traditionally, case studies were typically therapist-authored retrospective accounts. Contemporary approaches incorporate multiple perspectives. This includes patient and therapist narratives, researcher observations, and systematic data collection methods. Case studies can be beneficial for investigating exceptions to general trends and giving voice to underrepresented experiences in psychotherapy research. Case studies can be useful in knowledge transmission within communities of practice. There is a close connection between single case studies and psychotherapy as it is practiced since clinical competence necessarily is built case by case. Thus, case studies can be useful to integrate theoretical knowledge with practical application and thereby contribute to development of professional expertise, including practical wisdom and clinical flexibility. Since psychotherapy case studies often involve ethical dilemmas, they may be useful to help therapists to develop their ethical reasoning skills. Advice for how to do qualitative case study research are provided, highlighting practical and ethical implications.