The International Workers Unity-Fourth International (IWU-FI [UIT-CI in Spanish])) is a global revolutionary socialist organization, founded in Barcelona in 1997, with the merger of various currents that vindicate themselves followers of the political and theoretical legacy of Leon Trotsky and of one of the main leaders of Trotskyism post WWII, Nahuel Moreno.

The IWU-FI acknowledges itself as an organization that is part of the international Trotskyist movement. We strive for the reconstruction of the IV International founded by Leon Trotsky in 1938, but do not consider ourselves as being the IV International. We fight for the unity of the revolutionary Trotskyist or not, that support a principled revolutionary socialist program to rebuild that International and revolutionary parties in each country. The IWU-FI and its sections are in the service of that task rejecting all forms of self-proclamation and sectarianism.