Synaxarion, (pl. Synaxaria (Greek: Συναξάριον, from συναγειν, synagein, to bring together), is a term relating to compilations, lectionaries, and indexes that have had differing definitions over the centuries. Today, in the Orthodox Church, the Synaxarion is an abridged collection of the “Lives of the Saints,” intended for reading in public worship and to nourish the personal prayer life of the faithful.
Variously, the synaxaria in the earliest types included lectionary synaxaria of indexes of Biblical and other lessons, that is Biblical Lectionary pericopes that were to be read in church. Often these were listings according to the calendar year and the Paschalion cycle. These liturgical lectionaries grew to include complete texts of the Gospels and Epistles that led to the modern editions of the Gospels and Epistles.
The early index synaxaria also developed into lists of saints arranged in order of their commemoration anniversaries that often included such material as troparia and kontakia of liturgical calendars. By the tenth century, brief biographical notes were added to the calendar listings for the year which were summaries of those in the collections of the lives of saints (menologies). As the lessons of the Divine Office of the Orthodox Church were always of the lives of saints, the synaxarion became a collection of saints' lives. This developed into the modern Greek Synaxarion containing brief "Lives of Saints", that, among the Slavic nations, is more popularly known as the Prologue.
Among his works, St. Nicodemus the Hagiorite prepared a Greek edition of the Synaxarion of Constantinople during the late eighteenth century that included the memories of a number of saints, including most of the notable New Martyrs. Recent editions, which are based on the work of St. Nicodemus, enlarged upon his work. Thus, these editions include saints venerated by the local Orthodox Churches, including those of Russia, Romania, Georgia, Serbia, and Bulgaria, many of whom were glorified after the collapse of the communist regimes. These synaxaria also include many Western saints from the period of the undivided Church. Thus, the Synaxarion presently constitutes the most complete collection of lives of the saints of the Orthodox Church.