Power systems throughout the world are experiencing increasing levels of power electronics interfaced generation in their generation portfolio. As these devices have a significantly different dynamic behavior than conventional synchronous generators, it is expected that this trend will pose power system stability related challenges. This paper presents the results of a questionnaire conducted within the MIGRATE project. The aim of this questionnaire, to which more than 20 European transmission system operators (TSOs) responded, was to identify and prioritize these challenges. The TSOs identified challenges related to rotor angle stability (two), frequency stability (three), voltage stability (five), and power electronics interactions and resonances (two). In a follow-up survey, the TSOs were asked to rank the challenges based on their severity, probability of occurrence, and time of manifestation. The decrease of inertia was ranked the highest among the 11 issues. Additionally, the TSOs gave insight into current practices with regards to system monitoring and analysis. Based on the ranking, mitigation measures are currently being designed in order to facilitate an even higher amount of power electronics interfaced renewable energy sources in the power system.