In the field of sociological theory, after the decline of Parsons’ version of structural functionalism, Niklas Luhmann’s systems theory came to be seen as the major representative of systems thinking. While Luhmann’s autopoietic systems ontology is sophisticated and deserves serious consideration, the author argues that the prevailing identification of Luhmann’s constructivist-oriented approach with the systems approach itself is problematic mainly for two reasons. First, as the works of the Argentinian-Canadian systems theorist Mario Bunge demonstrate, the systems approach can be fruitfully based on (some version of) scientific realism. Second, the adherents to Luhmann’s constructivist epistemology in sociology seldom engage in a detailed examination of the various critiques of anti-realism offered by scientific and critical realists. Drawing on the literature on philosophy of science, especially the writings of Bunge and a few leading critical realists, the author suggests that a serious Luhmannian sociologist is obligated to provide more cogent and detailed discussions on philosophy of (social) science before taking an opinionated position on epistemology.