This paper gives an overview of the Church Slavonic – Chakavian traces (at the orthographical, phonological, and grammatical levels) in the two oldest Dubrovnik (and also Croatian) Latin-script prayer books: the Vatican Croatian Prayer Book (ca. 1400) and the Croatian Academy’s Dubrovnik Prayer Book (mid-15th century). Lexical characteristics and problems related to translation from the Latin source are also pointed out, when important for the orthographical, phonological, and grammatical analyses. The paper also concentrates on scribal errors in manuscripts, which gave evidence of the existence of Glagolitic and western Cyrillic patterns in the Dubrovnik Prayer Books, with special interest in Glagolitic–Cyrillic influence on the Latin script. Church Slavonic and Chakavian traces in morphology are mostly a result of direct transcription from the older patterns. An outline of some important syntactic characteristics related to morphological categories is represented in the paper. Special effort is given to the explanation of ikavism in the Dubrovnik Prayer Books. The linguistic analyses provided in the paper lead to the conclusion that there is a deep and centuries-long connection between the Croatian Latin and the Church-Slavonic culture and religious sphere.