This thesis finds its thematic focus in the foreign policy of Britain and France. Drawing on assumptions of social constructivism, it aspires to outline an independent vein within the analysis of ideas in foreign policy. _Guiding principles_ is the pivotal concept in our investigation, referring to _collectively held ideas embedded in national-political culture_. By way of historical study we attempt to seek out a set of guiding principles in post-war French and British policy; these principles are presented as a set of variables where France and Britain diverge. The second part of the thesis evaluates this typology against empirical data. Material is taken from debates preceding the invasion of Iraq in 2003, restrained to the political elites of government and parliament and focusing on textual sources. The analysis shows that while traditional French/British contrasts are largely supported by data, there was also intra-national variation over Iraq. This is particularly the case in Britain, where the Prime Minister, Tony Blair, is seen as expanding the British discourse by reuniting a French-derived _moral activism_ with a British penchant towards _efficiency_ and _enforcement_. In France, meanwhile, the President, Jacques Chirac, as well as the national assembly, are portrayed as champions of a selective approach to the Iraq issue, highlighting certain traditional principles while neglecting others. Our analysis concludes with a theoretical observation; while _guiding principles_ pose a foundational framework to national interest definition, they are sufficiently abstract to allow for a fair amount of political engineering.