Hydraulic fracturing for shale gas is a controversial issue in most countries. In these controversies discursive boundary work is a communicative strategy actors use to convince various audiences of their position. It involves the framing of facts in contrast to other kinds of arguments. In this article we develop the Dynamic Discourse Coalition (DDC) approach to study how discourse coalitions deploy boundary work to confirm, integrate, polarize or disintegrate their own and opposing discourse coalitions. The DDC approach enables a deeper understanding of the dynamics of controversies about hydraulic fracturing and similar contested technologies by illuminating the influence of communicative processes on policy formation. Based on an analysis of policy documents, academic reports, newspapers, interviews and websites we compare the dynamics of contesting discourse coalitions in The Netherlands and New York. This analysis explains why policy formed in different ways in the cases despite the apparent similarity of the discourse coalitions that emerged in the respective controversies.