Below, the events of World War I have the "WWI" prefix.
January 1915
January – British physicist Sir Joseph Larmor publishes his observations on "The Influence of Local Atmospheric Cooling on Astronomical Refraction".
January 1
WWI: British Royal Navy battleship HMS Formidable is sunk off Lyme Regis, Dorset, England, by an Imperial German Navy U-boat, with the loss of 547 crew.
Battle of Broken Hill: A train ambush near Broken Hill, Australia, is carried out by two men (claiming to be in support of the Ottoman Empire) who are killed, together with four civilians.
January 5 – Joseph E. Carberry sets an altitude record of , carrying Capt. Benjamin Delahauf Foulois as a passenger, in a fixed-wing aircraft.
January 12
The United States House of Representatives rejects a proposal to give women the right to vote.
A Fool There Was premières in the United States, starring Theda Bara as a femme fatale; she quickly becomes one of early cinema's most sensational stars.
January 17 – WWI: Caucasus Campaign – Battle of Sarikamish: Russia defeats Ottoman Turkey.
January 18 – Twenty-One Demands from Japan to China are made.
January 19
Georges Claude patents the neon discharge tube for use in advertising.
WWI: German Zeppelins bomb the coastal towns of Great Yarmouth and King's Lynn in England for the first time, killing more than 20.
January 21 – Kiwanis is founded in Detroit, Michigan, as The Supreme Lodge Benevolent Order Brothers.
January 23 – Chilembwe uprising: Baptist minister John Chilembwe initiates an ultimately unsuccessful uprising against British colonial rule in Nyasaland (modern-day Malawi).
January 24 – WWI: Battle of Dogger Bank: The British Grand Fleet defeats the German High Seas Fleet, sinking the armoured cruiser .
January 25 - The first United States coast-to-coast long-distance telephone call is facilitated by a newly invented vacuum tube amplifier, ceremonially inaugurated by Alexander Graham Bell in New York City and his former assistant Thomas A. Watson, in San Francisco, California.