This paper aims at investigating the social cleavages structuring the secular camp in Egypt, Tunisia, Algeria and Morocco. While the Islamist/Secular cleavage is a common characteristic of these four political party systems, the internal structuring of the Secular camp differs from one country to another. For instance, the regional/national cleavage is virtually non-existent in the Egyptian and Tunisian political fields, but fundamental in Algeria and important in Morocco, due to the politicization of the Amazigh identity in both countries. The socialist/liberal cleavage is highly structuring in Tunisia and Morocco, less in Algeria, and almost non-relevant in Egypt, where one can find both socialist and liberal parties in different competing electoral coalitions. Due to recent regime changes and the disbanding of their once hegemonic political parties, Tunisia an Egypt witness the existence of a cleavage opposing the old regime and the revolution, but this cleavage proved itself more determining in Egypt than in Tunisia, at least in 2011. Exploring the social forces acting within the secular camp of each of the four countries under study, this paper try to identify the factors explaining these differences: the politicization of the regional, linguistic or religious identities, the political role of the army and its relation with other dominant social forces, and the integration of the subaltern classes (workers and peasants) by the post-independence regimes.