The topic of this thesis is the abuse of a dominant position. The dominant position is regulated by the Competition Act from 2021. Prior to the enactment of the current Competition Act, the dominant position was regulated by the Competition Act from 2003. The paper will analyze the amendments to the old Competition Act, and the current provisions on the dominant position under the Act from 2021., as well as the most important provisions of the Treaty on the Functioning of the EU relating to the protection of competition. The third and fourth parts of the paper are focused on defining and analyzing the concept of dominant position and ways of determining and proving it. After that, in the central part of the paper, the notion of abuse of a dominant position is discussed and the most common forms of abuse of a dominant position are analyzed. As part of this paper, the decisions of the Croatian Competition Agency and the judgments of the European Court in the field of abuse of dominant position and distortion of competition are also attached as part of this paper.