The diploma thesis focuses on apposition and its syntactic and semantic characteristics in the headlines of Czech and English online media. In the theoretical part, the format of a headline is introduced as a part of written journalistic texts as well as significant Czech and English concepts about appositions are presented. The selected approaches are then united into a classification which is later used for the purposes of the linguistic analysis in the practical part. The aforementioned analysis deals with syntactic and semantic aspects of appositional units, classifies the language data and describes them in detail. The final chapter of the thesis contain the conclusion and offer the results of the linguistic analysis. KEY WORDS apposition, nominal apposition, nonnominal apposition, nominal phrases, clause, sentence, appositional constructions, appositives, headlines, Czech media, English media, online media, restrictiveness, non-restrictiveness