The organisation for the Nordic energy regulators, NordREG, has ordered this study to explore status of demand side flexibility among Nordic distribution system operators (DSOs). Demand side response is a question of mobilising potential flexibility in how and when end users choose to use energy, and how such flexibility can provide value to the network. Network value can be reduced or deferred investments, better system reliability or other system cost reductions. This report addresses concepts for utilising demand response and related regulatory issues. The report also includes an interview study among selected DSOs in the Nordic countries. This addresses current status, how flexibility can be a value for their business, what they see as barriers and planned activities relating to demand response.