This paper tries to explain the evolution of the phenomenon of non-religious in Portugal, understanding its relationship with the politics of secularism of the Portuguese state in the first decade and a half of the 21st century. In the first part, we will use the theories of secularization as the theoretical framework in order to understand how increasing levels of rationalization or existential security are related to the rise in the number of people who reported being indifferent, atheists or agnostics between 1999 and 2011. Then, due to the rise of the category “believer without religion” in Portugal, we will call on the religious individualization theory, namely the arguments of “believing without belonging” or “reflexive spirituality”, in order to grasp how they can help us to frame the sociological developments of non-religion in Portugal. Secondly, we propose the study of non-religion in the light of Portuguese secularism. We analyze in particular public policies usually associated with secular principles, for instance: the abortion referendum, the law on same-sex civil unions or the recent decree on gestational surrogacy. This seeming secularization of principles hides a strong dichotomy. On the one hand, public policies tend to be more secular, going along with the evolution of the non-religious universe. On the other hand, considering that the vast majority of Portuguese is still religiously affiliated, especially to Catholicism, or the existence of a Concordat with the Holy See, the state is compelled to a governance of intense negotiation and indispensable sharing of (public or symbolic) space with religions. These “twin tolerations” are manifested in religious education in public schools, public funding of religions, military or hospital chaplaincies or religious airtime in public service television. It is precisely this dynamic between secularization, secularism, and religiosity that we will try to unravel in this paper.