One of the key challenges arising from the recent increase in international involvement in post-conflict situations has been to establish security and to transfer responsibility to local institutions in ways compatible with principles of ownership, accountability and economic sustainability. While there is no lack of prescriptions for security transitioning, there has been little analysis of past efforts. The author suggests a list of criteria for the evaluation of success and failure of security sector reconstruction and reform in post-conflict situations. He also describes various dilemmas for external actors and concludes with a hypothesis on how the behaviour of external actors influences success and failure of security sector reconstruction and reform.