Professionals increasingly must collaborate very closely, such as through inter-professional work arrangements. This involves learning both "in" and "for" collaboration. Some educational researchers have turned to complexity science to better understand these learning dynamics. This discussion asks, How useful is complexity science for examining professional learning in collaboration? After introducing complexity principles that appear in accounts of professional practice and education, selected studies are presented that draw from complexity science to examine professional collaboration in fields of management, social and health care, and education. A critical discussion of these studies points out oversights and limitations. Complexity theory is concluded to offer useful insights for two areas: (1) articulating complexities of professional practice and knowledge and (2) providing educational support for professional knowing-in-undecidability. However, it is also argued that complexity analyses of professional collaboration could do much more to exploit the explanatory power of complexity concepts, by returning to rich dynamics of strong emergence in a sociomaterialist analysis, and by avoiding metaphorical uses of complexity. Used rigorously rather than romantically, complexity concepts may prove more useful not only in analysing political dynamics of collaborative professional practice, but also in opening new questions and approaches for future research in professional learning. (Contains 2 notes.)