Wind power is going through a very rapid development. It is the fastest growing power source in the world, the technology is being developed rapidly and wind power is supplying significant shares of the energy in large regions. The integration of wind power in the power system is therefore now an issue in order to optimise the utilisation of the resource and in order to continue the high rate of installation of generating capacity, which is necessary in order to achieve the goals of sustainabitity and security of supply. This development of the wind power from just being a negative load to have power plant like features of course also bring with it large challenges. These challenges include connection of wind farms to weak grids, securing power quality, reduction or elimination of power fluctuations, prediction of power output and changes in operating strategies of conventional power plants. Many of these challenges can be faced by the application of power electronics in wind turbines or in wind farms, but many of them will also require other technologies to be developed such as fuel cells and energy storage. The key issues for success is the utilisation of power electronics and information technology. The paper will, through examples (from Denmark and from finalised and current research work), highlight the challenges and present the current research direction.