Insular art includes fine art of Ireland and Great Britain from the middle of the seventh until the second half of the twelfth century. The subject matter of this paper is the first or early medieval period of the insular art which takes place between 650 and 850 years. Missionary activities were one of the most important factors that caused the cultural uprising which happened in the first phase of the insular art. Missionaries from Ireland and the Continent first had a crucial role in the Christianization of the Celts and the rest of the local population of Great Britain. After that, they also Christianised Angles, Saxons and Jutes who inhabited the British island in the fifth century. Not only have missionaries brought Christianity, but they also have introduced new art influences. Via their activity, the Christian iconography has been incorporated in the local tradition, from which the unique Hibernosaxon style in the book illumination developed. It is a style which took the abstract manner from the local tradition with the prevalent usage of the interlace and extremely stylized zoomorphic loops. Christian symbols and characters are also in the repertoire of the motives. They are modified extremely stylistically and two-dimensionally, similar to abstract ornaments. The development of the Hiberno-saxon style can be followed from simpler forms, which are found in the Book of Durrow, to its culmination present in the Book of Kells and the Book of Chad. At the same time, in the southern part of Britain, there are also Mediterranean influences in art brought on the island by Roman missionaries. Strictly under Mediterranean influences, manuscripts like Codex Amiatinus or St Augustine Gospels, were created. At the end of the seventh and the beginning of the eighth century, Hiberno-saxon and Mediterranean styles were becoming intertwined in certain cultural centres. Due to that, some manuscripts, for example, Book of Lindisfarne or Stockholm Codex Aureus, have features of both styles. Insular art had been on the peak in its first phase and, thanks to the missionary activities, influenced the art in the continental Europe.