The notions of Operational Leeway and Power to Act are often used as synonymous. Therefore, it is necessary to specify their relationships. Clinical approaches to work activities in psychology share with ergonomics a point of view according to which interventions must necessarily be anchored into the complexity of work situations, with the collaboration of various professionals. In order to better understand the developmental processes of professional activity, and the obstacles to these processes, Wisner borrowed from the activity theories of Vygotsky and Léontiev. The examination of relationships between Operational Leeway and Power to Act questions the conception of activity development, which has been put forward by ergonomists and psychologists. We discuss the links between subjectivity, activity and development, and the fact that organizational, individual, and collective operational leeway take their source in the development of the powers to act. The operational leeway thus gained could become instrumental in further developing powers to act in the subject’s activity. However, workplace interventions must be thought of as means to foster professional debates concerning different ways to think about, and act upon, operational dilemmas at work.