Supervision intended to support learning is of great interest in professional knowledge development. No single definition governs the implementation and enactment of supervision because of different conditions, intentions, and pedagogical approaches. Uncertainty exists at a time when knowledge and methods are undergoing constant development. This situation affects professions with high demands on precision and safety, and thus supervision and learning. The aim of this article is to explore the practice of supervision for learning professional knowledge of forensic specialists. The context is the Swedish National Laboratory of Forensic Science internal training program, which focuses on learning in daily work when the forensic trainee is assigned a supervisor. Ethnographic studies of supervisors and trainees in different forensic specialties were conducted. Practice theory is used to understand how supervision is planned and implemented to support professional development. Findings show that supervision by seasoned professional forensic specialists is significant for trainee learning. However, supervision is arranged, and performed differently, indicating various conditions for learning. Furthermore, the material set-ups of the professional practice prefigure the practice of supervision. Supervision is an area of expertise that needs to be cultivated and learned to maintain highly specialized professional knowledge in current time of change and uncertainty.