Orthodox (Eastern Churches) and Catholic (West) Church, although similar at the first sight, have much in common. That similarity between them is the main subject in this master's thesis. To be more exact, at the term of similarity, we mean at the in sacrament of Holy Order. It is well known that every religion has someone who, in the name of all believers, brings on sacrifices to the God(s) and is involved in proceedings the religious rituals. Those are the ones, who, by the laying on of their hands, get ordained in the Holy Order. For us, they are well known as: priests. From our experience we can see that the concept of priesthood, its essence is unknown to numerous. People often don't know what the real purpose of priests is and they see it only when priest celebrates Mass. Enigma of priesthood essence causes aspiration of exploration and deepening our understandings. I will try to show my own research. This master's thesis is made of six chapters which brings us to review of development of Holy Order, especially second rank of clergy: presbyters. First chapter brings us biblical foundation of Holy Order and its meaning in Old and New Testament. In second chapter is elaborated the progress of services and ranks of Holy Order throughout history. Third chapter brings us meaning of priesthood on Second Vatican Council and show us which changes have been made after it. Services and ranks of Holy Order in Eastern Churches are part of fourth chapter. Fifth chapter shows us valid Ordain rituals of priest in Eastern and Western Churches. Comparison of those two rituals are elaborate in sixth chapter.