During times of financial crisis and market stress, the role of different market players and the impact of institutional features are of critical concern. Ratings agencies have a prominent position in such considerations, and a significant debate asks whether their actions exaggerate, calm or have no influence on the turbulence of financial markets. Using high frequency financial data on foreign exchange and stock markets this project will inform this debate by exploring the influences of rating agency behaviour on market outcomes. The findings from this work will be of major interest to governments, regulators, investors and ratings agencies.