The Iron Front (German: Eiserne Front) was an anti-Nazi, anti-monarchist, and anti-communist paramilitary organization formed in the Weimar Republic. It was formed on 16 December 1931 by the Social Democratic Party (SPD) with the Allgemeiner Deutscher Gewerkschaftsbund, the Reichsbanner and workers' sport clubs originally to counter the right-wing Harzburg Front formed by the National Socialist German Workers Party, the Stahlhelm and the German National People's Party. The organization sought to engage the old Reichsbanner, the SPD youth organization, and labor and liberal groups as a united front. The SPD rallied to the Iron Front, held mass demonstrations, fought fascists in the streets, and armed themselves. This is more than the SPD leaders wanted, but SPD workers grew increasingly revolutionary. In 1933, the organization was banned.
Its logo, the Antifascist Circle (three arrows, pointing south-west/to the lower-left inside a circle) was designed by Sergei Tschachotin, former assistant to the physiologist Ivan Pavlov in 1931. It was designed so as to be able to easily cover Nazi swastikas. The meaning of the three arrows has been variously interpreted. One meaning is that they stood for the opponents of the Iron Front, the three enemies of social democracy: reactionaries (especially monarchists wanting to restore the Hohenzollern monarchy), Bolshevists, and fascism (the Nazis in particular), as seen in a 1932 election poster for the SPD. The present-day Reichsbanner Association says the arrows of the logo stood for the SPD, the trade unions and the Reichsbanner Schwarz-Rot-Gold, as well as for the political, economic and physical strength of the working class. The symbol was later adopted in the United States by the Young People's Socialist League (formed in 1989), and was kept as their logo until their disbandment in 2010.