The construction of the Spanish liberal state in the nineteenth century clashed with Catalonia, where social and political opposition forces prevailed. Catalonia was the most dynamic economic center of the peninsula, a place where cultural currents born beyond the Pyrenees rapidly expanded. European powers could not ignore the Catalan specificity. In the case of the French Republic, it posed added challenges: the existence of a French Catalonia -the Roussillon-; the presence of one of the biggest communities of French citizens abroad with substantial economic interests; and neighborhood border. The present investigation has sought to analyze which perception the French Government had about Catalonia, based on the information they got from their diplomatic agents. This study focuses in a key period in the late nineteenth century and early decades of the twentieth century, when the Catalan nationalism gathered strength and became a political phenomenon of broad social support. The objective of this study is to explain in detail the view or views of Catalonia these diplomatic agents transmitted, and check if they ended up being long-lasting cliches. This investigation has also tried to find out what attitudes were generated, what policy measures were taken and if we can identify a "French Catalan policy". This research was conducted mainly in French public archives, and to a lesser extent, in Catalan and Spanish archives. We have discovered French authorities gave importance to the Catalan working class movement, especially those currents with revolutionary character. Throughout the study we present the parameters from which it followed up this revolutionary working class and we expose how this influenced the relations between France and Spain. This PhD thesis is divided into two blocks. The first block analyzes the official view and the French policy regarding Catalan identity and the Catalan nationalist movement, distinguishing between the view conveyed by consular agents in Barcelona, Tarragona and Palma, and the French ambassador in Madrid. In terms of analysis, the episode of the military assault at Cu-Cut!, the Ley de Jurisdicciones and the constitution of the Catalan Solidarity stand out. The knowledge obtained about Catalan nationalists initiatives developed in Paris, little known in general, can be helpful in the future. The second block examines the monitoring and measures that the French Republic adopted regarding the Catalan revolutionary working class both in Catalonia and among refugee groups in France who lived there fleeing the Spanish repression. We have established the prominence of Catalan anarchists in revolutionary conspiracies among the Spanish community in France, their close links with what was happening inside Catalonia, and its integration into the European antimilitarist and freethinking movements. The attitudes of foreign governments regarding the Catalan national reality is still an unexplored field. The same applies to its impact on international relations. In this sense, this research aims to contribute to these two fields of study.