Historians of liberalism have tended to ignore or underplay the contribution of southern Europe. However, in the 1820s this part of the world was at the forefront of the struggle for liberal values. This essay explores the relationship between constitutional culture and religion during the liberal revolutionary wave that affected Portugal, Spain, the Italian peninsula and Greece, by examining parliamentary debates, the revolutionary press, literature targeting the masses, religious sermons and exile writings. It argues that rather than rejecting religion, liberals strove to find an accommodation between their values and revealed truth—they were convinced that no society could survive without religious morality. In this way, they developed a variety of religious attitudes that ranged from deism to forms of crypto-Protestantism without abandoning their established religions. At the same time, although they defended individual rights and freedom of expression against the opposition of the churches, and argued for reformed and enlightened forms of religiosity, most of them considered the religious uniformity of their societies advantageous and even opposed religious toleration.