The aim of this master's thesis is to examine the topic of using style guides in institutional translation, especially in the context of translation in the EU institutions. The theoretical part of the thesis first defines institutional translation and then describes the topic of translation in the EU institutions and of translation manuals and style guides in institutional translation in general and specifically in the EU. The empirical part is focused on the analysis of the Interinstitutional Style Guide as a set of rules and guidelines used in institutional translation in the EU institutions; the IISG is also compared with the grammar and spelling rules of the Czech language in the Czech Internet Language Reference Book by the Czech Language Institute of Czech Academy of Sciences. The thesis examines the observance rate of those rules in the Czech language versions of legal documents published in the Official Journal of the EU from 2004 to 2020. The analysis is conducted in a corpus compiled of EU legislative texts through ApSic Xbench. The results of the analysis are then compared to the occurrence of the examined language phenomena in a corpus of original Czech legal documents. The findings shall contribute to the research of the specificities of institutional translation, especially to the...