The topic examined in this article is not anti-semitism in itself, as illustrated by those who engage in it, but anti-semitism as brandished as a charge against real or alleged offenders. This approach is indispensable, the author argues, for a fuller understanding of how the notion of anti-semitism operates in political discourse and action. The author speaks in particular of the accusation of anti-semitism in cases where it can be shown that the behavior targeted is at least in part, and sometimes in great part, imaginary and constructed. The effectiveness of this ascribed anti-semitism depends on the capacity of those who construct it (precisely in order to denounce it) to make it appear plausible by connecting it, however indirectly, with tangible anti-semitic acts or declarations. The author explores a few cases from recent French experience in which the connection between what is denounced as anti-semitic discourse or activity and what has actually occurred is often tenuous, overblown, or, at the least, highly debatable. In such cases anti-semitism is constructed in an essentializing and a-historical manner, in such a way as to lump together disparate groups and individuals into a supposed current or milieu or nebula, portrayed in conspiratorial terms.