The case of cross-border metropolises (Lille, but also Strasbourg, Basel or Geneva) is a singular one: the border, although devalued and easily crossed, continues to exist (political, legal differences, etc.). In the case of the Eurometropolis Lille-Kortrijk-Tournai, are the public transport systems integrated? Or, on the contrary, do discontinuities persist? The aim of this chapter is to examine whether there is a border effect on mobility between France and Belgium, and, more specifically, between the three entities responsible for local mobility of the Eurometropolis Lille-Kortrijk-Tournai: The Métropole Européenne de Lille (MEL, also known as the ‘European Metropolis Lille’ in English), Flanders and Wallonia. Do integration factors in the Eurometropolis (devaluation of borders, absence of natural barriers, integrated economic functioning, urban continuity, etc.) combine with integration through the networks, notably public transport? To achieve our aim, we draw on several kinds of data: mobility surveys to examine differences between the various entities of the Eurometropolis; an analysis of integration relating to information and pricing; and, above all, a comparative measurement of public transport accessibility. Our investigations led us to question the role of the integrated public transport network within the Eurometropolis given cross-border mobility issues.