Defamation is the act of damaging another's reputation. According to recent legal research, defamation laws may be improperly used in many ways. Some of these uses profoundly affect the historian's work: first, when defamation laws protect reputations of states or nations as such; second, when they prevent legitimate criticism of officials; and, third, when they protect the reputations of deceased persons. The present essay offers two tests of these three abuses in legal cases where historians were defendants. The first test, a short worldwide survey, confirms the occurrence of all three abuses; the second test (an empirical analysis of twenty-one cases (1965-2000) from nine western European countries) the occurrence of the third abuse. Both tests touch on problems central to the historical profession; living versus deceased persons; facts versus opinions; legal versus historical truth; the relationship between human dignity, reputation, and privacy; the role of politicians, veterans, and Holocaust deniers as complainants; the problem of amnestied crimes. The second test - the results of which are based on verdicts, commentaries, and press articles, and presented in a synoptic table - looks closely into the complainants' and defendants' profiles, the allegedly defamatory statements themselves, and the verdicts. All statements deemed defamatory were about such contemporary events as World War II (particularly war crimes, collaboration, and resistance) and colonial wars. Both tests amount to two conclusions. The first one is about historians' professional rights and obligations: historians should make true, but privacy-sensitive or potentially offending, statements only when the public interest is served; otherwise, they should have a right to silence. The second conclusion concerns defamation itself: defamation cases and threats to sue in defamation have a chilling effect on the historical debate; they are often but barely veiled attempts at censorship.