The need for policymakers to understand science and for scientists to understand policy processes is widely recognized. However, the science-policy relationship is sometimes difficult and occasionally dysfunctional; it is also increasingly visible, because it must deal with contentious issues, or itself becomes a matter of public controversy, or both. Laura Diaz Anadon and her coauthors suggest that identifying key unanswered questions on the relationship between science and policy will catalyse and focus research in this field.