The objective of Task 25 is to analyse and further develop the methodology to assess the impact of wind power on power systems. The Task has established an international forum for exchange of knowledge and experiences related to power system operation with large amounts of wind power and has actively followed parallel activities with Transmission System Operators other R&D Task work. The participants have collected and shared information on the experience gained and the studies made up to and during the task. The case studies have addressed different aspects of power system operation and design, mainly: balancing, grid impacts and capacity credit of wind power. In the meetings, all participants have made presentations of the wind integration issues in their country, results so far and on-going activities. In the latest meetings presentations have been grouped to different topics to better dwell into the details of modelling challenges. In addition, there has been some telephone/web meetings for the journal articles and Recommendations report. In the Task 25 meetings, updates from other international work are also given (EU/TPWIND and SET-Plan, IEEE, IPCC). TSO collaboration is important for Task 25 work. There has been TSO participation in all meetings, with the participants from Canada, Denmark and Italy in most meetings and some other countries sending TSO participants in fewer meetings.