This thesis is a review of polytheistic religions in Istria during the Principate. It is based on available and relevant literature. The focus of the study is on the religion in Istria during the Principate, based on the architectural, epigraphic remains and remains of sacred plastic. With the establishment of colonies of Pola and Parentium and the introduction of municipalization, along with the settlement of Italics, the Roman pantheon was introduced to the peninsula in the 1st century BC. Three religions coexisted in Istria during the Principate, namely: the Roman religion, with which the imperial cult was associated, as well as the autochthonous and oriental religions. This thesis presents the most important deities for each religion, their role and in which places they were most present. Based on the created map and chart and according to the remains of epigraphic inscriptions an overview of the worship of deities in Istria was created. The thesis also emphasizes the imperial cult and the autochthonous religion which turns out to be very important as it was noted on the monuments after the arrival of the Romans and the introduction of writing to the peninsula. It appears either in pure form or in the form of interpretatio romana, and the highest intensity of worship is recorded in the south of Istria and on the eastern Istrian coast, at Alvona and Flanona.