Research evaluation has become routine and often relies on metrics. But it is now driven too much by the data and not enough by expert judgement. As a result, the procedures that were designed to increase the quality of research are now threatening to damage the scientific system. To support researchers and managers, five experts led by Diana Hicks, professor in public policy at Georgia Tech University, and Paul Wouters, director of CWTS at Leiden University, have proposed ten principles for the measurement of research performance: the Leiden Manifesto for Research Metrics.