Despite an increasing number of programs that aim to develop or educate leaders, the underlying processes involved in leader development or growth are not well understood. This study was undertaken to discover what factors or processes are involved in leader development for junior military officers, from their own perspective and in the natural context of their career and life experiences. Military officers (N = 51) from 5 different countries were interviewed using a standardized approach, and interview transcripts were analyzed according to the constant comparative method of grounded theory, as elaborated by Glaser and Strauss (1967). Consistently across the 5 countries, the core of the process model of leader development is the social interaction between the young officer and his or her significant others (soldiers, peers, and superiors). In the favorable case, officers end this process feeling secure, being able to flexibly adapt their overt behavior on an underdistanced–overdistanced continuum according to situational demands, and have a firm professional identity.