First Legion

First Legion may refer to:


 * The First Legion (1951 film) U.S. drama film
 * Legio I (Ancient Rome), see List of Roman legions
 * Legio I Adiutrix
 * Legio I Armeniaca
 * Legio I Germanica
 * Legio I Iovia
 * Legio I Isaura Sagittaria
 * Legio I Italica
 * Legio I Macriana liberatrix
 * Legio I Maximiana
 * Legio I Minervia
 * Legio I Parthica
 * 1st Legion Tercio "Great Captain Gonzalo Fernández de Córdoba", an infantry regiment in the Spanish Legion
 * 1st Legions Infantry Division (Poland), an infantry division in the Polish army
 * 1st Brigade, Polish Legions, an infantry brigade in the Austro-Hungarian army