Research has shown that develo ping shared identity is important for the success ful outcomes of mergers and acquisitions. However, developing a shared identity can be problematic when employees experience identity threat. Yet the complex nature as well as the causes and consequences of identity threat need to be further explored. In this chapter, we will address this gap by delineating three types of threat and the subsequent employees’ reactions to these threats. D raw ing upon acculturation and social identity theories, we propose a typ ology of identity threat and a model wherein employees’ perceived legitimacy of implementation decisions might trigger a particular type of identity threat and subsequent collective reactions. As such, we believe this chapter will provide a more differenti ated understanding of identity threat as well as a more nuanced insight to employees’ reactions during socio - cultural integration process by recognizing that identity threat can be experienced for different reasons with particular reactions. We conclude wi th recommendations for managerial practice.