Brexit is a coined word consisting of the words “Britain” and “exit”. It actually represents the intention of the United Kingdom to leave the European Union. The main purpose of this diploma thesis is to examine and present the effects of the withdrawal on the UK’s economy and on the future development of the European Union. During the writing of this thesis, several writing methodologies were used. The historical or descriptive method was used mostly in the first part of the thesis, where the historical development of the European Union is presented. Apart from that, the same method was used also to present the relationship between the United Kingdom and the European Union in general. The most frequently used method was the comparative analysis, which was used for comparing the four main economic indicators before the referendum on the withdrawal and after it. The statistical method was used for a more accurate description of the main economic indicators. Apart from the previously mentioned methods, integration theories were one of the main pillars of this diploma thesis. They aided in gaining insight into the background to the main political reasons for United Kingdom's withdrawal from the EU in the first place. The main aims of the diploma thesis have been achieved, despite the great problems encountered when gathering accurate data, especially in the economic field. The lack of accurate data has led to the fact that neither economists nor politicians can accurately predict the actual impact of the withdrawal on the UK’s economy. Because the actual effects will be seen in a couple of years, only predictions have been made, based on the noticeable changes to the economy so far.