The Triangle Factory fire in New York City on March 25, 1911 was a major public-affairs crisis in the United States which led to improved working conditions for sweatshop workers as well as better fire inspections.

The Triangle Shirtwaist Company occupied the top three floors of the Asch building, a ten-story building at the intersection of Greene Street and Washington Place in New York City. The company employed approximately 500 workers, mostly young female immigrants working fourteen-hour days, in the manufacture of clothing.

The conditions of the factory, while unacceptable by today's standards, were typical of the time. Flammable textiles were stored throughout the factory, smoking was widespread, illumination was provided by open gas lighting, and there was no fire extinguishing equipment.

On the afternoon of March 25, 1911, a fire started on the eighth floor. The workers on the tenth floor were alerted and most of the employees on these two floors were able to evacuate. But the message did not reach the ninth floor in time.

The ninth floor had two doors leading to stairwells. One of these was already filling with smoke and flames by the time the workers realized there was a fire. The other door had been locked as was standard practice to keep workers from leaving early. There was an exterior fire escape but it quickly collapsed under the weight of the women trying to escape. An elevator which serviced the floor stopped working cutting off the last means of safe escape.

Realizing there was no better means of escape, some of the women broke out windows and jumped to the ground nine floors below. Others forced open the elevator shaft doors and jumped down the open shaft. Few survived either experience. The remainder stayed on the floor until the fire reached them. The fire department arrived quickly but was unable to fight the flames; they had no ladders that reached higher than the sixth floor. The death toll was 145; 91 died in the fire and 54 died by jumping.

While the factory had not been particularly noted for its harsh treatment of workers, in the aftermath of the tragedy, the fire was a boost for the cause of factory safety and became a symbol for the nation's growing labor movement, notably the International Ladies Garment Workers Union. The owners, Max Blanck and Isaac Harris, had fled to the building's roof when the fire began and survived. They were later acquitted in a criminal trial but lost a subsequent civil suit in 1913. Another person affected was Frances Perkins, the future Secretary of Labor under Franklin Roosevelt, who was among the witnesses who watched the fire from the streets below.

The tragedy was the subject of a 1978 movie, The Triangle Factory Fire Scandal.