The article focuses on Slovenia’s entry into the European Union from a longer time perspective. It outlines the history of the European Economic Community (EEC) as the precursor of the European Union (EU), the transformation of the EEC into the EU and the emergence of Slovenia as an independent national state. The article takes the development of the EU and Slovenia in the 1990s as the central time period. The accession negotiations, adaptation of institutions and legislation to the EU rules and norms, and the consequences of the Slovenian entry in the EU are the main topics highlighted by the article. Time-wise, this ends with Slovenia becoming the EU member in 2004. By directing the attention to the institutions, the article begins by presenting the field of political history and new institutionalism, explaining how a long life of institutions, their formal activities and the narratives they create help shape in a significant way political processes, including actions of individual politicians and political parties, as well as actions of voters. The article also indicates current research trends and presents the key findings by some of the Slovenian and foreign researchers in connection with the political history, transition from socialism to parliamentary democracy and key democratic system institutions.