Research on physical education (PE) teachers’ (de)motivating styles has predominantly relied on self-reported data from students and to a lesser extent from teachers. While less frequently used, observational research serves as a crucial complement to these self-reports, offering a more authentic assessment of PE teachers’ (de)motivating styles. This chapter begins by providing an overview of the currently available observational measures for examining PE teachers’ (de)motivating behaviours from a self-determination theory perspective. It then focuses specifically on the SIS-PE-Coder, an observational instrument designed to assess these behaviours through a circumplex view. This chapter addresses three main questions: (1) Does the SIS-PE-Coder represent the circumplex model of four styles (i.e. autonomy-support, structure, control, chaos) and eight approaches (i.e. participative, attuning, guiding, clarifying, demanding, domineering, abandoning, and awaiting)?; (2) How do PE teachers’ (de)motivating styles assessed with the SIS-PE-Coder relate to student-reported measures of PE teachers’ (de)motivating styles?; and (3) How do PE teachers’ (de)motivating styles assessed with the SIS-PE-Coder relate to student motivational outcomes (i.e. need-based experiences and motivation)? This chapter concludes by discussing practical implications and offering recommendations for future research.