This study of principals’ professional identity formation is part of a longitudinal study of 12 practicing principals who are participants in the Swedish National Head Teacher Program during 2014-2017. The aim of the three-year program is for principals to acquire knowledge and skills in three interrelated areas: school legislation, management by goals and objectives, and school leadership. While the overall purpose of the study is to study the effects of the program, this paper will report on the first phase, a survey to all principals attending a leadership development program and interviews with 12 selected principals. The ISSPP interview protocol will be used to examine the role of leadership preparation in the development of professional identity, which is defined as “identities which individuals use to make sense of and enact [their] roles” (Scribner and Crow, 2012, p. 246). These first interviews aim at understanding “…what influences a leader’s behaviors and what drives a leader’s willingness and ability to take on and enact creative and effective leadership in a high-stakes, dynamic knowledge society” (Scribner and Crow, 2012, p. 245). The analysis of these ‘first-phase’ interviews, reported on at ECER in Porto 2014, will be followed by interviews in 2015 and 2016.