Despite its increasing importance, reflection in its collective notion has mainly been studied as a temporary way of actors stepping back to question their daily work and its underlying assumptions. In this study we ask how we can conceptualize collective reflection as process in its sustainable notion in organizations over time. Building on process thinking, we draw on an in-depth, longitudinal case study of introducing lean management to a hospital’s pluralistic emergency care unit. We propose a process model of collective reflection consisting of various collective activities of the two practices of “stepping-back” and “stepping-in” over time. In order to develop our understanding of the “how” of collective reflection, we differentiate the two practices according to the purpose of their reflexive activities, the position of the main collective actors and according to who reflects about what when and how. Further, we analyze the interaction of “stepping-back” and “stepping-in” over time. The two dynamics observed (a content-related linkage between the two practices resulting in a shift from “stepping-in” towards “stepping-back” activities over time and an orchestration of the various “stepping-back” activities over time) will help to explain how organizational reflexivity becomes a sustainable process over time. These insights contribute to the existing debate on reflection as a collective, dialogical practice.