Interdisciplinary research is essential for the study of complex systems, and so there is a growing need to understand the factors that facilitate collaboration across diverse fields of study. In this exploratory research, we examine the formation of self-organized project groups and the structure of collaboration networks at the Santa Fe Institute’s Complex Systems Summer School. Using data from all iterations of the summer school from 2005 to 2019, comprising 779 participants and 304 projects, we investigate the factors influencing group formation. We find that group formation at the Summer School based on gender, position, affiliation, country of study, and discipline is largely consistent with random mixing. Similarly, using standard network measurements, we find that no single discipline is more prone to interdisciplinary collaboration than any other; nor do participants from any particular discipline exert stronger influence in the network. While our results point to a high degree of interdisciplinary collaboration overall, project topics from the social and behavioral sciences are significantly over-represented. This could be due to a higher level of baseline interest in, or knowledge of, social and behavioral sciences, or the common application of methods from the natural sciences to topics in the social sciences. Consequently, future research should explore this discrepancy further and examine whether it can be mitigated through policies aimed at making topics in other disciplines more accessible or appealing for collaboration.