The palaeography of the first Slavic script - the Glagolitic script - is being published in English language for the first time. Unlike former historiography-based palaeographic textbooks, this study is linguistically substantiated. After presenting the elemental historical and philological knowledge on the creation of the script and its relation to the parallel Slavic script - the Cyrillic - the author goes on to distinguish the development of those linguistically-based segments (e.g. graphemes) from the means that optimize the transfer of linguistic message through the visual writing system. The evolution of letter forms is being observed in the long process of minusculization. The coordination of letters in lines and the readjusting of their forms to the four line system turned out to be the 'spiritus movens' of the changes not only in the letter forms but in the script's entire visual appearance as well. At the focus of interest, there are the oldest Macedonian, Bulgarian, Czech and Croatian Glagolitic texts of the 10th and the 11th century.