This Master Thesis aims to answer the question why the EU foreign policy-makers decided toimplement the Eastern Partnership (EaP). As the EU foreign policy decision-making processis based upon consensus between all EU Member States, an argumentation analysis isconducted to find the arguments that the policy-makers use to convince the others. By usingHabermas’ Theory of Communicative Action, the arguments are categorized into pragmatic(security and economic interests), moral (humanitarian values) or ethical-political (culturalvalues) logics. The research material consists of official documents and statements of the EUinstitutions. Then, the arguments are evaluated as whether they can be said to be legitimate,‘mobilizing’ arguments: intelligible, appropriate and true. The main result is that even if allargumentation categories are used by policy-makers, none of the categories can be said to becompletely legitimate. Therefore, an ideological perspective is a possible complement to thecategories within the Theory of Communicative Action. This perspective would possibly addto the understanding why the EaP was implemented.