Glagolitic inscriptions and graffiti are first-class epigraphic sources for understanding the complex historical circumstances and sociointellectual events in the Slavic ethnic space during the early Middle Ages. It is an area of Pannonia and the former Avar Khaganate marked by a strong Carolingian influence. This influence extends to the Croatian and Slavic principalities on the eastern Adriatic coast, which are in the sphere of Byzantine interest, which is confirmed by historical sources and archaeological findings. Of particular importance are the earliest preserved Glagolitic epigraphs that testify about the use, development and spread of the Glagolitic alphabet among the Slavs. Unlike literary and church liturgical works, epigraphic monuments, due to their memorable function, are proof of literacy and culture in a precisely defined area, thus achieving exceptional scientific and historical value. In addition to the presentation of Cyril and Methodius research in Croatian science and a historical overview of the work area as signed to the topic, the paper presents a detailed palaeographic analysis and description of the most significant Glagolitic epigraphic monuments in Central and Southern Europe. The early influence of Byzantine culture among Croats is evidenced by Glagolitic and Cyrillic monuments from Dalmatia, which testify in favor of the spread of the Glagolitic alphabet along the southern path from the Macedonian cultural circle. The spread of the Glagolitic alphabet along the northern path under the influence of the Carolingian culture is evidenced by Zalavar's fragments that confirm the use of the Glagolitic alphabet in Pannonia at the end of the 9th century. These two directions of expansion are in the wake of the consideration of the Split synodal writings from 925. and some other documents that led to the conclusion that Dalmatia, as well as some parts of Slavonia, are areas where Glagolitic literacy first appeared. The appearance of Glagolitic literacy in Istria and Kvarner is some what later and is well covered.