This dissertation analyzes the professionalization of new ventures. Thereby, it takes up a key moment in this professionalization process, namely a new venture's first succession event where the founder is replaced with a professional CEO. In order to foster our understanding of this moment, it adopts three different perspectives: First, assuming a cognitive stance, it integrates the succession event within the broader literature of organizational change. Second, adopting a sensemaking perspective, it sheds light on how founders construct narratives to make sense of the role transition they undergo in the succession event. Third, embracing an upper echelons view, this dissertation shows how the different founder post-succession roles relate to the changing dynamics within the top management team and how these changes in turn influence strategic decision-making outcomes.