Book excerpt: Poe Yu-ze Wan argues for a critical realist and systemist social ontology, designed to shed light on current debates in social theory concerning the relationship of social ontology to practical social research, and the nature of 'the social'. It explores the works of the systems theorist Mario Bunge in comparison with the approach of Niklas Luhmann and critical social systems theorists, to challenge the commonly held view that the systems-based approach is holistic in nature and necessarily downplays the role of human agency.