Notwithstanding more than a century of policies aimed at school democratisation, the education system in French-speaking Belgium is characterised by the persistence of sharp social inequalities in outcomes. These inequalities reflect considerable phenomena of segregation observed between streams and between schools (Lafontaine, 2005; Lafontaine et al., 2003; Jacobs et al., 2009). The structural causes of this situation are well documented in the literature (see in particular Lafontaine and Monseur, 2011; Dumay, Dupriez and Maroy, 2010; Danhier et al., 2014) and researchers generally agree that segregation between school environments can be attributed in large part to the combined effects of a quasi-market regulation of the system and a considerable institutional differentiation of educational provision. Following a brief presentation of the definition of school segregation that will be used in this chapter, we review these two main mechanisms and their political and socio-historical roots. We then describe several indicators of social, academic (i.e., according to students' educational attainment) and ethnic segregation in the education system in French-speaking Belgium and bring out how, paralleling the spread of such indicators, the concept of segregation has gradually entered public debate on the school. In the final section we address the policies that have been adopted to combat school segregation and the accompanying social inequalities.