The aim of this paper is to determine whether British and German sea fisheries policies have been shaped by domestic factors or by European Union (EU) institutions. To achieve this aim, British and German perceptions of the EU's Common Fisheries Policy (CFP) were compared using two alternative theories of EU integration: Moravscik's Liberal Intergovernmentalism and Pierson's Historical Institutionalism. The perceptions of three sets of respondents—fisheries scientists, fishers, and politicians—were investigated in each country to determine whether they saw the CFP as a means of attaining their own nation's domestic fisheries agenda (as Liberal Intergovernmentalism would argue), or as an institutional champion of European fisheries as a whole (as might be predicted by Historical Institutionalism). The article concludes that although there were elements of both theories evident in each country's perceptions, British perceptions were more strongly indicative of Historical Institutionalism than Liberal Intergovernmentalism, and German perceptions were more strongly indicative of Liberal Intergovernmentalism than Historical Institutionalism. This difference is exemplified in Britain's euroscepticism (which sees EU institutions as obstacles to British fisheries’ interests), and Germany's environmentalism (which sees EU institutions as synchronising with Germany's national priorities).