Comparative studies of agricultural biotechnology regulation have highlighted differences in the roles that science and politics play in decision-making. Drawing on documentary and interview evidence in the United States, the United Kingdom, and Germany, we consider how the “regulatory cultures” that guided national responses to earlier generations of agricultural biotechnology have developed, alongside the emergence of genome editing in food crops. We find that aspects of the “product-based” regulatory approach have largely been maintained in US biosafety frameworks and that the British and German approaches have at different stages combined “process-based” and “programmatic” elements that address the scientific and sociopolitical novelty of genome editing to varying degrees. We seek to explain these patterns of stability and change by exploring how changing opportunity structures in each jurisdiction have enabled or constrained public reasoning around emerging agricultural biotechnologies. By showing how opportunity structures and regulatory cultures interact over the long-term, we provide insights that help us to interpret current and evolving dynamics in the governance of genome editing and the longer-term development of agricultural biotechnology.