This paper analyses the policy mix for urban transition by drawing on insights from studies in institutions and path dependence. It sheds new light on the role of institutions and actors in creating a policy mix for sustainable city districts, which has not been systematically addressed in the current debate on policy mix. The interaction and trade-offs between policy instruments for energy efficiency in buildings in the city district of Hammarby Sjostad are analysed historically. The key findings are that long periods of increasing returns in existing technological systems and the institutions that have supported them have created different types of lock-ins' (behavioural, policy and industry). A systemic approach to developing a framework for policy mix analysis is necessary to address the relationship between various lock-ins'. (c) 2015 The Authors. Environmental Policy and Governance published by ERP Environment and John Wiley & Sons Ltd