We present the reader with the proceedings of the 27th International Congress of Onomastic Sciences. The congress took place in Kraków on August 22–27, 2021. Its main initiator was the late Professor Barbara Czopek-Kopciuch, who had passed away in 2020. It was an undertaking of scientific institutions from three Slavic countries: the main organiser in Poland was the Institute of Polish Language of the Polish Academy of Sciences, especially the Department of Onomastics, and the Faculty of Polish Studies of the Jagiellonian University in Kraków, the Committee of Linguistics of the Polish Academy of Sciences; in Slovakia – Ľudovít Štúr Institute of Linguistics of the Slovak Academy of Sciences in Bratislava, the Faculty of Arts of the Matej Bel University in Banská Bystrica, and Faculty of Education of the University of St. Cyril and St. Methodius in Trnava; in Czechia – the Czech Language Institute of the Czech Academy of Sciences.