December 21 (Eastern Orthodox liturgics)

• Forefeast of the Nativity of Christ.[1][note 2]

• Martyr Theomistocles of Myra in Lycia (251)[1][3][note 3][note 4]
• Virgin- martyr Juliana of Nicomedia,[6][7] and with her 500 men by the sword,[8][9] and 130 women by beheading.[10][11] (304)[1]
• Venerable Macarius the Faster, Abbot of Khakhuli Monastery (c. 1034)[1][12]

• Saint Honoratus of Toulouse, born in Spain, he succeeded St Saturninus as Bishop of Toulouse in France (3rd century)[13]
• Saint Severinus of Trier, Bishop of Trier in Germany (c. 300)[13][note 5]
• Martyrs John and Festus, martyrs honoured in Tuscany in Italy.[13]
• Saint Baudacarius, A monk at Bobbio Abbey in the north of Italy (650)[13]
• Saint Hincmar, Archbishop of Reims (882)[14][15]
• Saint Beornwald of Bampton (Bernwald), a righteous priest in Bampton in Oxfordshire in England (10th century)[13]
• Saint John Vincent, born in Ravenna, he became a monk at St. Michael in Chiusa, then a hermit on Monte Caprario, finally he became Bishop nearby (1012)[13]

• Saint Peter of Kiev, Metropolitan of Kiev and Moscow, Wonderworker of All Russia (1326)[1][16][17]
• Saint Juliana, Princess of Vyazma (Novotorzhok) (1406)[1][18][19]
• Blessed Procopius of Vyatka, Fool-for-Christ (1627)[1][note 6]
• Saint Anton II of Georgia, Catholicos Patriarch of Georgia (1827)[21]
• Saint Philaret (Theodosius in schema), Metropolitan of Kiev (1857)[1]
• Righteous-Virgin Yulianiya Solvychegodska (17th century)[22][23]

• Repose of Blessed Peter “the Nose,” of Kama (c. 1938)[1]
• Repose of Schemamonk Michael of Harbin (1939)[1]
• Finding of the relics (1950) of New Monk-martyr Ephraim of Nea Makri (1426)[1][note 8]
• Repose of Mother Stavritsa the Missionary, missionary in Kenya (2000)[1][29]

• 
  St. Juliana of Nicomedia.
• 
  St. Peter of Kiev, Metropolitan of Kiev and Moscow, Wonderworker of All Russia.
• 
  Icon of St. Tryphon of Vyatka and Procopius Vyatka (17th century, Vyatka (Kirov) Museum)

• December 21/January 3. Orthodox Calendar (PRAVOSLAVIE.RU).
• January 3 / December 21. HOLY TRINITY RUSSIAN ORTHODOX CHURCH (A parish of the Patriarchate of Moscow).
• December 21. OCA - The Lives of the Saints.
• The Autonomous Orthodox Metropolia of Western Europe and the Americas (ROCOR). St. Hilarion Calendar of Saints for the year of our Lord 2004. St. Hilarion Press (Austin, TX). p. 1.
• December 21. Latin Saints of the Orthodox Patriarchate of Rome.
• The Roman Martyrology. Transl. by the Archbishop of Baltimore. Last Edition, According to the Copy Printed at Rome in 1914. Revised Edition, with the Imprimatur of His Eminence Cardinal Gibbons. Baltimore: John Murphy Company, 1916.

Greek Sources

• Great Synaxaristes: (in Greek) 21 ΔΕΚΕΜΒΡΙΟΥ. ΜΕΓΑΣ ΣΥΝΑΞΑΡΙΣΤΗΣ.
• (in Greek) Συναξαριστής. 21 Δεκεμβρίου. ECCLESIA.GR. (H ΕΚΚΛΗΣΙΑ ΤΗΣ ΕΛΛΑΔΟΣ).

Russian Sources

• (in Russian) 3 января (21 декабря). Православная Энциклопедия под редакцией Патриарха Московского и всея Руси Кирилла (электронная версия). (Orthodox Encyclopedia - Pravenc.ru).
• (in Russian) 21 декабря (ст.ст.) 3 января 2013 (нов. ст.). Русская Православная Церковь Отдел внешних церковных связей. (DECR).