The presumed financial benefits of mergers & acquisitions (M&As) often do not materialize. At the same time, M&As are reported to create a host of negative reactions on the part of the employees involved. In recent years, these circumstances have led many scholars to use the social identity approach (SIA) in order to better understand the group psychology of M&As. This paper reviews recent M&A research inspired by the SIA and derives three general lessons that are explained in some detail: First, post-merger identification is important for M&As integration and success. Second, M&As pose a threat to organizational identification. Therefore, and third, if you have to merge – merge right.