Today’s session is about expert surveys. Expert surveys have become a popular tool to measure across time and space a wide array of political phenomena, from party positions to the quality of democracy. Expert surveys allow to study a large variety of phenomena. They are quick, they are not expensive, and they allow a general idea on different topics: the position of parties on European integration, the position on the left/right scale, the quality of democracy, and so on. Yet, recently, there was a lot of criticism against these expert surveys. The debate is double: one is about the reliability of the measure, and the other is about its validity. Are the results accurate? Is it possible to rely on experts’ judgments and what exactly do such surveys measure? To tackle these issues, two specialists are present. Jan Rovny (Sciences Po, CEE & LIEPP) draws from his experience as one of the principal investigators of the Chapel Hill Expert Survey on party positioning to reassess the validity/reliability of such instruments. René Lindstädt (Head of the School of government, University of Birmingham), discusses the nature of the measurement problems such data raise.