Shtrafbats (Russian: штрафбат, штрафной батальон) were Soviet penal battalions that fought on the Eastern Front in World War II.

The shtrafbats were greatly increased in number by Joseph Stalin in July 1942 via Order No. 227 (Директива Ставки ВГК №227). Order No. 227 was a desperate effort to re-instill discipline after the panicked routs of the first year of combat with Germany. The order—popularized as the "Not one step back!" (Ни шагу назад!, Ni shagu nazad!) Order—introduced severe punishments, including summary execution, for unauthorized retreats.

In his order, Stalin also mentioned Hitler's successful use of penal battalions (also known as Strafbataillon) as a means to ensure obedience among regular Wehrmacht units.

Pursuant to Order No. 227, the first penal battalions were originally authorized a strength of 800 men; penal companies were also authorized, consisting of between 150 and 200 men per company. In addition to the battalions already serving with Armies, other battalions, subordinated to Fronts (the equivalent of Army Groups), were introduced. The first penal battalion deployed under the new policy was sent to the Stalingrad Front on August 22, 1942, shortly before German troops reached the Volga river. It consisted of 929 disgraced officers convicted under Order No. 227 who had been demoted to the lowest enlisted rank and assigned to the penal battalion. After three days of assaults against the Germans, only 300 remained alive.

The order entitled 'Status of Penal Units of the Army' (Положение о штрафных батальонах действующей армии) of November 26, 1942, by Georgy Zhukov (then a Deputy Commander-in-Chief), formally standardized Soviet penal units. Penal battalions or shtrafbats were set at 360 men per battalion, and were commanded by mid-range and senior Red Army officers and political officers (politruks). Penal companies (штрафная рота, 100 to 150 per unit) were commanded by sergeants (NCOs) and privates.

Penal units consisted of two types of personnel: permanent and temporary. Permanent personnel were staff officers, company commanders, platoon leaders, political officers, and other junior commanders. Temporary personnel were the shtrafniki (punishees) who were sent to the unit for their crimes or wrongdoings in order to redeem themselves with their service.

In some penal units like the 8th Separate Penal (Officer) Battalion, platoons sometimes had up to 50 men, companies comprised 300 men, and the battalion could be as big as 850 men; which implies that a penal battalion was sometimes larger than a regular rifle battalion of the Red Army. Note that on paper, the battalion was to be commanded by a Colonel with two deputies, a chief of staff, and a political officer. The companies were to be commanded by Majors and their platoons by Captains. This is probably because in this instance, the shtrafniki consisted of former officers of the Red Army.

The total number of people convicted to penal units from September 1942 to May 1945 was 422,700. Very few of them were known to have survived the war.