The article addresses the various uses of expert knowledge during the controversy over shale gas in France and in Quebec (Canada). Cross-fertilization between policy analysis and science and technology studies demonstrates that political uses of expertise better explained the policymaking process in focusing on two specific utilizations: strategic ignorance and politics of time. Using data from press analysis, interviews, reports and documentation analysis, the article shows that social movements can also use strategic ignorance to support their environmental claims and that mastering the pace of the controversy and the policy debates enabled actors to better support their policy claims. The French case illustrates those two arguments while the Quebec case provides a more tradition account of State/Industry's utilization of knowledge production to delay decision and divert opposition.