Despite the initial function of hashtags as tools for sorting and aggregating information according to topics, the social media currently witness a diversity of uses diverging from the initial purpose. The aim of this article is to investigate the communicative functions of hashtags through a combined approach of literature review, field study and case study. Different uses of hashtags were subjected to semantic analysis in order to disclose generalizable trends. As a result, ten communicative functions were identified: topic-marking, aggregation, socializing, excuse, irony, providing metadata, expressing attitudes, initiating movements, propaganda and brand marketing. These findings would help to better understand modern online discourse and to prove that hashtags are to be considered as a meaningful part of the message. A limitation of this study is its restricted volume.