The liturgical calendar used in the Orthodox Church and Orthodox celebrations dates back to the remote times of antiquity. The structure of the calendar was decisively formed in the Byzantine period and its use was upheld by tradition until the 20th century. This article describes the organization of the Orthodox calendar. The calendar is divided into three cycles, which designate the most significant holidays, as well as customs and habits observed by believers. The basic course is the daily, weekly and yearly cycle. The daily cycle consists of seven prayers that occur at the same time of day and night. The weekly cycle includes the seven days of the week starting with Sunday, which is the first and at the same time the last day of the week on a symbolic level. The Orthodox religion as-sociates particular days of the week with remembering the mystery of faith, a saint, or a group of saints. The liturgical week is an icon, in the middle of which the Orthodox place Jesus Christ, thus it is often called the Weekly Passover, which symbolically invokes the history of salvation. The annual cycle is divided into moveable and immoveable feasts (de-rived from Easter). The Orthodox Church appoints them according to spiritual rather than historical order. The spiritual order displays God’s plan to save humanity.