This dissertation shows that and explains why two European Union (EU) Member States, namely France and the United Kingdom (UK), differ in the degree of internalisation of political conditionality. The dissertation is divided into two parts. The first part assesses the degree of internalisation of political conditionality. Following a three-fold measurement framework, the thesis examines French and British policies, legal documents and behaviour. The analysis of behaviour concentrates on four cases of EU aid sanctions: Madagascar 2009, Mozambique 2009, Nicaragua 2008 and Zimbabwe 2002. France and the UK differ significantly. France has not officially endorsed political conditionality, generally does not insert human rights clauses in its developing agreements, and is recurrently among the donors which take a soft stance in response to recipient governments’ abuses. The UK has adopted a fully-fledged policy requiring partner governments to respect human rights and basic democratic principles, has consistently included human rights clauses in its development agreements and often belongs to the group of hardliners in favour of the application of aid sanctions. The second part of the dissertation explains these differences. Given the complexities of aid decision-making, the thesis adopts an “analytic eclectic” approach and tests four alternative hypotheses derived from realism, international constructivism, liberalism and sociological institutionalism. The examination of the cases studies and more than 100 interviews with diplomats, aid officials and representatives from nongovernmental organisations show that the higher accountability of aid decisionmakers and social pressure by like-minded donors (in particular Nordic countries) have played the most significant role in generating deeper internalisation of political conditionality by the UK. While organisational cultures cannot explain the extent of internalisation of political conditionality, their differences are helpful to understand the characteristics of the cases when political conditionality is applied more reluctantly. Evidence is not sufficient to confirm the hypotheses based on material interests, Commonwealth influence and aid modalities.