This article investigates and identifies certain religious and related social conditions of the genesis and development of Calvinism. It therefore treats Calvinism as religiously and otherwise socially conditioned rather than, as prevalent in the current sociological literature, as solely or mostly conditioning in religious as well as political, economic, and cultural terms. The article argues and demonstrates that the religious and cognate social conditions of original Calvinism essentially consist of the Ancien Régime of religion, church, and society overall in Europe, and more precisely in France. It therefore identifies Calvinism as initially the product of and subsequently the attempt at reinstituting the ancient religious and social Régime, as indicated or adumbrated by the blueprint (and title) of Calvin’s key theological treatise. Specifically, the article rediscovers and reveals Calvinism in the light of being both the effect and the restoration of the medieval theocracy, called the Christian Republic and the like, as the Ancien Régime of religion and society, through establishing Calvinist theocratic and thus non- or quasi-democratic republics. The article intends to contribute to understanding, explaining, and predicting better the social causes, functions, and effects of Calvinism generally, particularly its religious and related conditions and outcomes.