The topic of this final paper is the origin, organization, and operation of the fundamental institutions of the European Union defined by the Lisbon Treaty. The emphasis is on the seven main institutions, and, in particular, three fundamental ones (institutional triangle), which make up the European Commission, the European Parliament and the Council of the European Union. Their history, organization and operation are explained for each institution separately and the process of adopting EU legislation is explained within the chapters on those institutions. The Lisbon Treaty, signed on 13 December 2007 and put into force at the end of 2009, reformed the institutional framework of the European Union, and in particular its legislative framework. With this treaty, the European Parliament was given new powers within the framework of legislation, which made it equal with the Council of the European Union in the decision-making process related to the work of the European Union and the way in which funds are spent. Parliament's ability to make and implement decisions has increased as it was given the power to elect the head of the Commission. After introducing and analysing the EU institutions, the conclusion is made on the positive and less positive effects of the Lisbon Treaty on the structure of the institutions and the legislative framework of the European Union.