Sustainable success calls for contextually ambidextrous organizing. According to theory, this entails enabling simultaneous high levels of exploration and exploitation within a subsystem. The practices involved in enabling contextual ambidexterity form a major and relatively unexplored leadership challenge. Our main aim is to draw on a combination of ambidexterity and complexity theory insights to understand how contextual ambidexterity emerges in dynamic contexts. We contribute to the literature on the role of leadership in enabling contextual ambidexterity by exploring the daily practices leaders enact to stimulate exploration and exploitation as well as to shift dynamically between them to (re)gain contextual ambidexterity. We present the results of two qualitative studies exploring leadership in project-based organizations where the pressure for contextual ambidexterity is relevant. We show that in responding adaptively to environmental stimuli, leaders shift between practices to emphasize exploitation or exploration to (re)gain the needed high levels of both, and their enactments are bounded by the conditions of keeping exploration and exploitation simultaneously high. We discuss the implications of these findings for understanding contextual ambidexterity as a dynamic accomplishment that emerges in everyday interactions, the role of leaders in enabling contextual ambidexterity, and the need for HR managers to support leaders in enacting this dynamic form of leadership.