Integration is crucial to interdisciplinary and transdisciplinary work and it therefore deserves perennial attention by scholars and practitioners of such work. Few have thought so carefully, deeply, and tenaciously about integration as Julie Thompson Klein. In this article, we recount the development of Klein's thinking on integration, from her early stepwise model in 1990 to her current socio-linguistic model. After summarizing Klein's views, we compare the socio-linguistic model to a more recent view of integration known as the IPO (input-process-output) model. We show how these two models of integration relate to one another, and then we demonstrate their complementarity using an example of integrative argumentation from a Toolbox workshop. We conclude that we can understand instances of cross-disciplinary integration better with both models than with only one or the other. This theoretical stereoscope opens new avenues of research about the types of integrative relations collaborators use, what is involved in social/rhetorical integration, and the extent to which it is feasible to specify all of the parameters in an instance of integration.