3rd Legions' Infantry Regiment (Polish: 3. Pulk Piechoty Legionów; 3 pp Leg.) was an infantry unit of Polish Legions in World War I, Polish Army and the Home Army. It existed in 1914–1939 and 1944–1945.
The regiment was formed in the autumn of 1914, out of soldiers of Eastern Legion, which was dissolved on September 21, 1914, after most its soldiers had refused to swear allegiance and obedience to the Emperor Franz Joseph I of Austria. Reinforced with additional volunteers from Austrian Silesia and Austrian Galicia, it took part in the Battle of Galicia as early as October 1914. The regiment fought in several important battles, such as the Battle of Rafajlowa, Battle of Mołotków, Battle of Kostiuchnówka, Battle of Rarańcza and the Battle of Kaniów. Disarmed by the Germans after the Battle of Kaniów (May 1918) the regiment was recreated by Polish authorities in early 1919. It fought in Polish–Ukrainian War (1918–19) and Polish–Soviet War of 1920.
In the Second Polish Republic Third Legions Infantry Regiment was at first stationed in the garrisons of Łuków and Grodno. Transferred to Jarosław, it became part of 2nd Legions Infantry Division from Kielce.
During the Invasion of Poland, the regiment was part of Łódź Army. It fought the advancing Wehrmacht in central Poland, from the area of Skierniewice through the Kampinos Forest to Modlin Fortress, surrendering on September 29, 1939.
The regiment was created once again in mid-1944 by the Home Army of the District of Radom–Kielce. During Operation Tempest it was part of Second Home Army Legions Division, and was dissolved in January 1945.