The objective of the present thesis was to investigate organisational members’ reactions to change as result of a merger. How do people react when their own group’s content and composition changes? How does that affect the extent to which they define themselves as members of the (new) group, and think as well as act in terms of that group membership? The scope of the study was to extend previous intergroup research on mergers (e.g., Haslam, 2001; Terry, 2001) by understanding changing identification processes and intergroup relations as two aspects that play a key role in merger adjustment. Thereby, special emphasis was put on change and the dynamic nature of social psychological processes. I applied a longitudinal design to examine an ongoing higher education merger that involved a university and a polytechnic.