The Battle of the Frontiers comprised battles fought along the eastern frontier of France and in southern Belgium, shortly after the outbreak of the First World War. The battles resolved the military strategies of the French Chief of Staff General Joseph Joffre with Plan XVII and an offensive interpretation of the German Aufmarsch II deployment plan by Helmuth von Moltke the Younger, the German concentration on the right (northern) flank, to wheel through Belgium and attack the French in the rear.

The German advance was delayed by the movement of the French Fifth Army (General Charles Lanrezac) towards the north-west to intercept them and the presence of the British Expeditionary Force (BEF) on the French left. The Franco-British troops were driven back by the Germans, who were able to invade northern France. French and British rearguard actions delayed the Germans, allowing the French time to transfer forces on the eastern frontier to the west to defend Paris, culminating in the First Battle of the Marne.