The question of the role of modern law in triggering social change is of particular importance in societies where customs and norms support the marginalization of some social groups. The conventional view supported in the literature is that the success of the formal law is constrained by the system of informal rules and values which support the prevailing customs, and the law therefore appears as a ‘dead letter’. It has been, therefore, largely recognized that the custom often acts as a powerful hindrance to equity-increasing changes. The first two chapters of the thesis aim at mitigating this pessimistic scenario. We develop two models which formally show that a progressive legal reform can, under certain conditions, shift the conflicting custom in the direction intended by the legislator. Formal law then acts as an outside anchor that exerts a ‘magnet effect’ on the custom. We illustrate our insights using examples on inheritance, marriage, and divorce in Sub-Saharan Africa and India. In the second chapter, we also show analytically that, under certain conditions, a gradual reform better serves the interests of the marginalized. We therefore argue that radicalism in legal reform may defeat its own purpose. One of the conditions to achieve the ‘magnet effect’ described in our models is the identification of agents with the new law. In the third chapter of the thesis, we focus on the adherence of agents to a pro-women legal reform in Morocco, the reform of the Family Code which is religious-inspired legislation. We use a unique database created from a survey we conducted in Morocco in 2008 to provide some evidence about the factors which drive conservative positions with respect to a progressive legal reform. In order to explain the identification of agents with the law, we mainly focus on three specific factors: education, location and religion. Contrary to what naïve beliefs would suggest – rural men with a low level of education and an intense religious practice express a lower support of the new Family Code –, we find that there is no straightforward relation between the three aforementioned factors (education, location and religion) and the support of the new legislation. Rather paradoxically, conservative positions are observed among educated people, when they are very religious. Finally, in the last chapter, we use the same database as for chapter 3 in order to study intra-household decisions concerning children’s education. We focus on the religiosity of both spouses in order to understand how this could impact on the participation of mothers in decisions. We use a measure of the intensity of religious practice as a proxy of parents’ religiosity. We find a positive and significant correlation between the intensity of religious practice of the mothers and their participation in decisions concerning their daughters’ education. This result is essentially true for poorly or non-educated women which suggest that religion acts as a substitute to education. Religious faith motivates mothers to participate in decisions concerning their daughters’ education mainly and there exists a spillover effect that makes them more concerned with the education of their sons as well. We do not find a clear significant correlation between the intensity of the religious practice of the fathers and their wives’ participation in decisions concerning their children’s education. We essentially explain these main results by analyzing the action and the discourse of religious movements and associations active in Morocco.