Security sector reform addresses two main challenges: (1) assisting institutions capable of providing security for the state and its citizens and (2) ensuring appropriate governance of these institutions in accordance with the principles of democracy and civilian oversight. This report is based on a study prepared as an input in a policy debate on the role of security sector reform in Norwegian assistance to peace building in developing countries. The report reviews the evolution of thinking around external assistance to security sector reform, and discusses the policies and programmes of the main donor agencies. The report also provides an overview of Norwegian support to security sector reform. This is followed by a case study of Southern Africa. The final section provides suggestions and recommendations for the future role of security sector reform in Norwegian support to peace building and development.