This book unveils the role of a hitherto unrecognized group of men who, long before the International Brigades made its name in the Spanish Civil War, also found reasons to fight under the Spanish flag. Their enemy was not fascism, but what could be at times an equally overbearing ideology: Napoleon's imperialism. Although small in number, British volunteers played a surprisingly influential role in the conduct of war operations, in politics, gender and social equality, in cultural life both in Britain and Spain and even in relation to emancipation movements in Latin America. Some became prisoners of war while a few served with guerrilla forces. Many of the works published about the Peninsular War in the last two decades have adopted an Anglocentric narrative, writing the Spanish forces out of victories, or have tended to present the war, not as much won by the allies, but lost by the French. This book takes a radically different approach by drawing on previously untapped archival sources to argue that victory was the outcome of a truly transnational effort.