- Dec 1 Boston Braves MLB franchise owner James Gaffney buys the Allston Golf Club on Commonwealth Avenue, Boston with a plan to construct a ball park there; ground breaking for Braves Field starts on March 20, 1915
- Dec 3 First Balkan War: The Naval Battle of Elli takes place.
- Dec 3 Gerrit Brinkman becomes 1st Dutch traffic officer
- Dec 3 Turkey, Serbia, Montenegro, Greece & Bulgaria sign weapons pact
- Dec 5 The Triple Alliance among Italy, Austria, and Germany (originally signed in 1882) is renewed for six years, beginning in 1914, a move inspired by instability in the Balkans
- Dec 6 China votes for universal human rights
- Dec 7 Bust of Queen Nefertiti found in El-Amarna, Egypt
Germany's War Council
Dec 8 Wilhelm II of Germany calls 'War Council'
Dalén Awarded Physics Nobel
Dec 10 Nobel Prize for Physics awarded to Gustaf Dalén for inventing automatic regulators for gas accumulators for lighthouses and buoys
- Dec 12 Rudolf Friml and Otto Harbach's musical "Firefly" premieres in New York City
- Dec 16 1st US postage stamp picturing an airplane, 20 cent parcel post, issued
- Dec 16 Austria-Hungary engage in conflict with Serbia
- Dec 16 First Balkan War: The Ottoman Navy is defeated by the Royal Hellenic Navy at the Battle of Eli
- Dec 17 Albania's de facto independence from the Ottoman Empire is recognized at the London Conference of Ambassadors
Bare Bones of the Great Ape-Man Hoax
Dec 18 Piltdown Man, later discovered to be a hoax, is supposedly found in the Piltdown Gravel Pit, by Charles Dawson
- Dec 23 Aswan Low Dam in Nile begins operation again, after being raised for the first time
Assassination Attempt on Lord Charles Hardinge
Dec 23 Indian revolutionary underground in Bengal and Punjab, headed by Rash Behari Bose attempt to assassinate Viceroy of India Lord Hardinge, by throwing homemade bomb into Viceroys's Howdah (elephant carriage) during ceremonial procession in Delhi. Although wounded, the Viceroy survives. Investigations lead to the Delhi conspiracy trial.