This thesis is a contribution to the study of French foreign policy in the time of “old diplomacy” in Northern Europe. Aiming to fill a gap, the object of investigation is French foreign policy in the Baltic area between 1871 and 1914 (from the French defeat during the Franco-Prussian War to the outbreak of the First World War). Particular attention is directed at the assets of the French diplomacy at work in the Baltic Sea: naval military planning, financial loans and culture. Since the period was dominated by the diplomatic isolation that Bismarck had placed France with the aim to prevent her from creating any kind of alliance to embark in a war of revenge against Germany, France carried out a policy of making ententes and alliances in order to break out from this isolation. However, in her attempt to emerge, France was challenged by Germany especially in relations with Denmark and Sweden. Although French foreign policy was able to use the loan as an instrument to secure a success with Russia by establishing a military treaty in 1892, but France did not succeed to attract and influence Sweden in the same way because of the risk of her turning to Germany. Also strongly challenged by Germany in Denmark, French foreign policy could not stop the willingness of Denmark to adopt a policy of neutrality. But, because of her intervention between Russia and Great Britain in the Dogger Bank incident in 1904, French diplomacy succeeded to gain the support of the British fleet in the case of a naval war in the Baltic Sea for operations against the German coast. Bringing together Russia and Great Britain for a naval cooperation in the case of a war in the Baltic Sea was, without any doubt, not only the most audacious and difficult task for French foreign policy, but also a sign of its strong revival. However, this Russo-British naval cooperation could not be converted into practice because of the geographical specificities of the Baltic Sea and the difficulties of naval military planning. Adressing this aspect, this thesis reveals the fundamental mistakes of the naval theoreticians who were defending naval theories based on land military theories and experiences.