The Red Shirts or Redshirts of the Southern United States were white supremacist paramilitary terror groups that were active in the late 19th century in the last years of, and after the end of, the Reconstruction era of the United States. Red Shirt groups originated in Mississippi in 1875, when anti-Reconstruction private terror units adopted red shirts to make themselves more visible and threatening to Southern Republicans, both whites and freedmen. Similar groups in the Carolinas also adopted red shirts.

Among the most prominent Red Shirts were the supporters of Democratic Party candidate Wade Hampton during the campaigns for the South Carolina gubernatorial elections of 1876 and 1878. The Red Shirts were one of several paramilitary organizations, such as the White League in Louisiana, arising from the continuing efforts of white Democrats to regain political power in the South in the 1870s. These groups acted as "the military arm of the Democratic Party".

While sometimes engaging in violent acts of terrorism, the Red Shirts, the White League, rifle clubs, and similar groups in the late nineteenth century worked openly and were better organized than the underground terrorist groups such as the Ku Klux Klan. They used organization, intimidation and force to achieve political purposes of restoring the Democrats to power, overturning Republicans, and repressing civil and voting rights of freedmen. During the 1876, 1898, and 1900 campaigns in North Carolina, the Red Shirts played prominent roles in intimidating non-Democratic Party voters.

According to E. Merton Coulter in The South During Reconstruction (1947), the red shirt was adopted in Mississippi in 1875 by "southern brigadiers" of the Democratic Party who were opposed to black Republicans. The Red Shirts disrupted Republican rallies, intimidated or assassinated black leaders, and discouraged and suppressed black voting at the polls.

Men wearing red shirts appeared in Charleston, South Carolina, on August 25, 1876, during a Democratic torchlight parade. This was to mock the waving the bloody shirt speech by Benjamin Franklin Butler of Massachusetts, in which he was falsely claimed to have held up a shirt stained with the blood of a carpetbagger whipped by the Ku Klux Klan during the Reconstruction Era. "Waving the bloody shirt" became an idiom in the South, attributed to rhetoric by Republican politicians such as Oliver Hazard Perry Morton in the Senate, who used emotional accounts of injustices done to Northern soldiers and carpetbaggers to bolster support for the Republicans' Reconstruction policies in South Carolina. The red shirt symbolism quickly spread. Suspects accused in the Hamburg Massacre wore red shirts as they marched on September 5 to their arraignment in Aiken, South Carolina. Martin Gary, the organizer in South Carolina of the Democratic campaign in 1876, mandated that his supporters were to wear red shirts at all party rallies and functions.

Wearing a red shirt became a source of pride and resistance to Republican rule for white Democrats in South Carolina. Women sewed red flannel shirts and made other garments of red. It also became fashionable for women to wear red ribbons in their hair or about their waists. Young men adopted the red shirts to express militancy after being too young to have fought in the Civil War.

State Democrats organized parades and rallies in every county of South Carolina. Many of the participants were armed and mounted; all wore red. Mounted men gave an impression of greater power and numbers. When Wade Hampton and other Democrats spoke, the Red Shirts would respond enthusiastically, shouting the campaign slogan "Hurrah for Hampton". This created a massive spectacle that united and motivated his followers.

Red Shirts sought to intimidate both white and black voters into voting for the Democrats or not at all. Their goal was to restore Democratic rule and white supremacy. The Red Shirts and similar groups were especially active in those states with an African American majority. They broke up Republican meetings, disrupted their organizing, and intimidated black voters at the polls. Many freedmen stopped voting from fear, and others voted for Democrats under pressure. The Red Shirts did not hesitate to use violence, nor did the other private militia groups. In the Piedmont counties of Aiken, Edgefield, and Barnwell, freedmen who voted were driven from their homes and whipped, while some of their leaders were murdered. During the 1876 presidential election, Democrats in Edgefield and Laurens counties voted "early and often", while freedmen were barred from the polls.