Foreign Legion (French Légion étrangère), unit of the French army consisting of volunteers of other nationalities. Frenchmen are legally barred from joining the legion as enlisted men. Most of the officers, however, are French. The legion was established in 1831, during the reign of King Louis Philippe, as a regiment trained for service in Algeria. The primary function of this unit has traditionally been to preserve order in the French overseas possessions, but it may be sent wherever French forces are needed. The headquarters of the legion was in Sidi Bel Abbès, Algeria, for 120 years. In 1962, however, the independent Algerian government demanded its withdrawal. Headquarters is now located in Aubagne, France.

Nationals of any country other than France may enlist if they are between the ages of 18 and 40 and are physically qualified. Backgrounds and personal histories are not investigated, and, except for minors, no identification papers are required. Known war criminals, murderers, and deserters from the armed forces of allies of France, however, are rejected. A legionnaire enlists for an initial term of five years, at the end of which time he is eligible for French citizenship. Once citizenship is obtained, the legionnaire may qualify for a commission if he meets the educational requirements for officers.

After service in Algeria the legion took part in colonial campaigns in many French colonies, especially in North Africa and Indochina. It fought in the Crimean War (1854-56), in Italy against the Austrians (1859), in Mexico in support of Emperor Maximilian, and in the Franco-Prussian War. During World War I it served with distinction on many fronts and was the most decorated unit of the French army. The legion fought in Norway and in France at the beginning of World War II. After the fall of France in 1940 many legionnaires joined the Free French forces of General Charles de Gaulle. Their heroic defense of Bir Hakeim in Libya in 1942 brought the legion new honors. Reorganized after World War II, the legion subsequently saw active service in Indochina, Korea, and North Africa. Large numbers of German war veterans enlisted in the legion immediately after World War II. In 1946, however, the maximum number of German legionnaires was fixed at 25 percent of the total strength.

Other nations have also maintained foreign legions. The best known of these is the Spanish one that Francisco Franco used as advance shock troops during the Spanish Civil War.