The 1999 Helsinki Summit marks one of the most momentous events in Turkish political history. The declaration of Turkey as an official candidate country for the EU in 1999 helped the EU to make a profound impact on the modernization of Turkish politics, as since then, Turkey's domestic politics have been approached by the EU not as an external issue but as an area of concern which needs to be closely scrutinized. This study seeks to shed light on what domestic factors in Turkish politics -i.e. political parties, civil society, political tradition and culture and the military establishment mediated the democratisation requirements laid out by the Copenhagen political criteria and what impacts the Copenhagen political criteria have had on Turkish politics since 1999, in the post-Helsinki era. In doing this, based on Europeanization studies, the study employs a conceptual framework comprising three-steps; Europeanization, goodness of fit and mediating factors. The study is believed to be particularly useful to academics and students of Turkish politics who would like to have more insight into the recent EU reforms in Turkish politics.