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 adaptation of the German Aufmarsch II deployment plan by Helmuth von Moltke the Younger. The German concentration on the right (northern) flank, was to wheel through Belgium and attack the French in the rear.

Plan XVII was the name of a "scheme of mobilization and concentration" that was adopted by the French Conseil Supérieur de la Guerre from 1912 to 1914, to be put into effect by the French Army in a war between France and Germany. It was a plan for the mobilisation, concentration and deployment of the French armies, to make possible an invasion of either Germany or Belgium or both, before Germany completed the mobilisation of its reserves simultaneous with a Russian offensive.