Scholars of traditional Western donors have frequently asked, 'Why is aid given?' With the emergence of numerous new donors after the end of the Cold War, this question has a new significance. One group of these new donors are the countries of post-communist Central and Eastern Europe. Within the literature that has developed in recent years to analyse their foreign aid programmes, Poland is surprisingly understudied despite being the most significant international actor in the region. This thesis addresses this gap by investigating the origins and development of the Polish foreign aid programme since 1989. This focus on a single country enables a comprehensive longitudinal analysis so far also missing from the literature. The thesis develops and applies an analytical framework that focuses on the diffusion of international norms and policies into the national policy-making process. Through this framework, the thesis identifies the sources of foreign aid policies, the mechanisms through which sources exerted influence on the policy-making process and Polish opportunities to influence the international agenda. The thesis applies the framework to foreign aid policy-decisions across the post-Cold War period and enables an assessment of the extent to which Poland's 'return to Europe' provided opportunities and constrictions for foreign policy-making. The analytical framework looks beyond the focus on the 'EU factor' prevalent in the CEE donor literature, while maintaining comparability with these studies' findings. The focus on competing explanations is a central contribution that results in several original findings. The thesis demonstrates the substantial influence of the United States on Polish thinking about aid provision. The evidence also suggests that direct interaction between countries is crucial for the implementation of international norms and policies. Highlighting the importance of interaction between member states contributes a novel perspective not just on EU policy-making about development cooperation, but also on foreign policy. This leads to the conclusion that Poland as a donor has been a 'good pupil of bad behaviour', learning from the examples of traditional donors that non-compliance and national preferences are acceptable. The thesis also introduces the argument that CEE donors are not as different from traditional donors as so far portrayed by the literature. Non-compliance with international commitments is prevalent among Western donors and national foreign-policy considerations motivate their aid flows. However, traditional donors have the advantage that their foreign policy priorities are easier to reconcile with the priorities of development cooperation. The main difference lies in the insufficient domestic capacities of Central and Eastern European donors to use aid as an effective foreign policy tool due to the legacy of the communist era.