1378

January–December

• March - In England, John Wycliffe tries to promote his ideas for Catholic reform by laying his theses before Parliament, and making them public in a tract. He is subsequently summoned before the Archbishop of Canterbury, Simon of Sudbury, at the episcopal palace at Lambeth, to defend his actions.
• April 9 - Following the death of Pope Gregory XI, and riots in Rome calling for a Roman pope, the cardinals, who are mostly French, elect Pope Urban VI as the 202nd Pope.
• July - Revolt of the Ciompi: Discontented wool carders briefly take over the government of Florence.
• August 4 - Gian Galeazzo Visconti succeeds his father, Galeazzo II Visconti, as ruler of Milan.
• September - A contract is set up between Richard le Scrope, 1st Baron Scrope of Bolton and the mason Johan Lewyn, for the construction of Bolton Castle.
• September 20 - Unhappy with Pope Urban's critical attitude towards them, the majority of the cardinals meet at Fondi, elect Clement VII as antipope, and establish a rival papal court at Avignon. This split within the Catholic Church becomes known as the Western Schism.
• November 10 - Estimated appearance date of Halley's Comet.
• November 29 - Charles IV, Holy Roman Emperor, dies in Prague. He is succeeded by his son, Wenceslaus, as King of Bohemia, but the office of Holy Roman Emperor falls into abeyance, until Charles's son Sigismund is crowned in 1433.

  Date unknown

• Holy Roman Emperor Charles IV visits his nephew Charles V of France, to publicly celebrate the friendship between their two nations.
• France, Aragon, Castile and León, Cyprus, Burgundy, Savoy, Naples and Scotland choose to recognise Antipope Clement VII. Denmark, England, Flanders, the Holy Roman Empire, Hungary, northern Italy, Ireland, Norway, Poland and Sweden continue to recognise Pope Urban VI.
• Dmitri Donskoi of Moscow & Vladimir resists a small invasion, by the Mongol Blue Horde.
• Tokhtamysh dethrones Timur Malik, as Khan of the White Horde.
• Kara Osman establishes the Turkomans of the White Sheep Dynasty at Diyarbakır, in present-day southeast Turkey.
• The Turks capture the town of Ihtiman, in west Bulgaria.
• Uskhal Khan succeeds his father, Biligtü Khan, as ruler of the Yuan Dynasty in Mongolia.
• Balša II succeeds his father, Durađ I, as ruler of Zeta.
• Tai Bian succeeds Zhao Bing Fa, as King of Mong Mao.
• Da'ud Shah succeeds his assassinated nephew, Aladdin Mujahid Shah, as Bahmani Sultan in present-day southern India. Da'ud Shah is assassinated in the same year, and is succeeded by Mohammed Shah II.
• Sa'im al-Dahr is hanged, for blowing the nose off the Sphinx.