Wind power capacity in Europe is growing at an impressive rate and is expected to continue its growth in the near future. Power system operation with increased wind power penetration is exposed to a number of challenges, prominent among them is operation without undermining the level of adequacy and security provided by current power systems.The thesis deals with key questions related to the reliability of power systems with high wind power penetration, namely the question of wind power capacity credit calculations. It describes probabilistic calculation methods in detail, with a special focus on sources of statistical uncertainties in wind power in-feed time series.Furthermore, a "wind penetration fingerprint" of twelve European countries is presented in this work as a basis for the discussion on balancing market mechanisms being appropriate for high wind power penetration.