The Experimentation Platform will enable product groups at Microsoft and developers using Windows Live to innovate using controlled experiments with live users. Such a platform will enable testing new ideas quickly using the best-known scientific method for establishing causality between a feature and its effects: randomized experimental design. The basic methodology in controlled experiments is to expose a percentage of users to a new treatment, measure the effect on metrics of interest, and run statistical tests to determine whether the differences are statistically significant, thus establishing causality.