Ambidexterity research has presented a range of structural and contextual approaches for implementing a dual orientation across organizations. Much less is known about the preceding process through which organizations decide to adopt an ambidextrous orientation. In this paper we focus on this first step—the charter definition process through which the activities and responsibilities of an organizational unit are agreed. Most prior studies implicitly assume that senior executives at some point identify the need to become ambidextrous and subsequently design supportive structures and contexts to implement their choice. Based on an inductive multilevel case study of four alliances, we show how this mandated (or top-down) charter definition process can be complemented with an alternative emergent (or bottom-up) charter definition process in which frontline managers take the initiative to adopt an ambidextrous orientation in their part of the organization. This emergent process is important because it enables frontline managers to respond in a timely manner to changing requirements of which senior executives are still unaware. We use the findings from our case study to develop potentially generalizable observations on the level of initiation, the tensions, the management approaches to deal with the tensions, and the outcomes that characterize this emergent charter definition process. We then put forward a multilevel process framework of how organizations initiate an ambidextrous orientation, and we discuss theoretical implications for the general ambidexterity literature, the nascent dynamic view on ambidexterity, and the broader research on how charters in organizations evolve.