The doctoral thesis about Hieratikon of priest Lucian Petroaia brings to the researchers’ attention, the most important book of service of the orthodox priest. From a historical perspective, the author has carefully identified and investigated all editions of the Hieratikon printed in Romania, from 1508 to the present; from the point of view of analyzing the content of the Hieratikon, he follows the evolution of the order of the Holly Liturgy over 500 years, often comparing the text of the Romanian Hieratikon with that of the Greek Hieratikon and the Slavic Slujebnik. The interdisciplinary approach emphasizes the essential role that the Orthodox liturgical cult had for the assertion of Romanian culture, in the landscape of the European and Universal culture.     Priest Lucian Petroaia is an associate professor in Liturgical Theology at the Faculty of History, Philosophy and Theology at “Lower Danube” University in Galaţi and at “Justinian Patriarch” Faculty of Orthodox Theology at University of Bucharest, Romania.