ENThe purpose of the paper is to understand what factors drive transformation of the national innovation system of a transition economy. The case study is based on 32 semi-structured, in-depth interviews with major stakeholders of Lithuanian innovation system. The paper contributes to national innovation system literature by revealing the importance of the human agency role in the process of institutional change. It sheds light on institutional entrepreneurship as the key mechanism that stimulates institutional change and the overall transformation of the innovation system. It shows that institutional entrepreneurs reinforce institutional change through various internal and external pressures. The qualitative findings have important implications for academics, policy makers and managers in all transition countries. Keywords: National innovation system, transition economy, institutional entrepreneurship, qualitative case study. [From the publication]