The T-34 was a Soviet medium tank that had a profound and lasting effect on the field of tank design. Although its armour and armament were surpassed later in the war, it has been often credited as the most effective, efficient, and influential tank design of World War II. At its introduction, the T-34 possessed an unprecedented combination of firepower, mobility, protection, and ruggedness. Its 76.2 mm (3 in) high-velocity tank gun provided a substantial increase in firepower over any of its contemporaries; its heavy sloped armour was difficult to penetrate by most contemporary anti-tank weapons. First encountered in 1941, German tank general von Kleist at the time called it "the finest tank in the world" and Heinz Guderian confirmed the T-34's "vast superiority" over existing German armour of the period.

T34 may refer to:

• T-34, a 1940 Soviet tank
• T34 (classification), a disability classification used in para-athletics
• T-34, a rock band featuring Al Murray
• T34 (microprocessor), a z80 compatible Zilog microprocessor
• T34 Calliope, a 1943 U.S. tank-based rocket launcher
• Beechcraft T-34 Mentor, a 1953 U.S. military trainer aircraft
• Frostbite with tissue necrosis (ICD-10 code T34)
• T34, a variant of the U.S. T29 Heavy Tank
• T.34 (1978–1980), a predecessor to the musical group This Window
• Slingsby T.34 Sky, a glider from Slingsby Aviation
• Pratt & Whitney T34, turboprop aero engine