The question of “civil religion” constitutes the impensé of French secularism,and this is necessarily so due to the term's ideological function. Using Jean-Jacques Rousseau's definition--revisited by sociologists--, this article considersthe relationship between secularism and civil religion at two periods. Duringthe period 1901-1908, two types of secularism opposed each other: the first,close to civil religion, was dominant until 1904; the second, which emerged in1905-1908 (the laws on the separation of Church and State) distanced itselffrom it. The second period is the beginning of the twenty-first century, whenelements of a “lay-Catholic” civil religion are thwarted, however, by severalfactors. In conclusion, the author offers several avenues of comparisonbetween American civil religion and French civil religion.