Guenter Lewy (22 August 1923 – 24 March 2026) was a German-born American author and political scientist who was a professor of political science at the University of Massachusetts Amherst. His works spanned several topics, but he was most often associated with his 1978 book on the Vietnam War, America in Vietnam, and several controversial works that deal with the applicability of the term genocide to various historical events, where Lewy denied both the Romani genocide and the Armenian genocide.

In 1939, he migrated from Germany to Palestine. After World War II, he migrated to the United States to reunite with his parents. Lewy earned a BA at City College in New York City and a MA and PhD at Columbia University. He was on the faculties of Columbia University, Smith College, and the University of Massachusetts Amherst. He later lived in Washington, D.C., and was a frequent contributor to Commentary. Lewy died in Bethesda, Maryland on 24 March 2026, at the age of 102.

Lewy was born in Breslau, Germany, (now Wrocław, Poland) on 22 August 1923. At the age of nine, he joined a German-Jewish scouts organization called Die Greifen (lit. "the griffins"), which he has suggested was important in shaping his desire for an academic career. Described by Lewy as a "quasi-Romantic" group, Die Greifen emphasized music, literature, and song, particularly Landsknechtlieder, encouraging the youths to avoid becoming "Spiessbürger" ("philistines"). By 1938, as persecution of Jews in Germany increased, Lewy began to lobby his family to leave Germany behind. After Kristallnacht, in November 1938, when his father was interned in Buchenwald for four months and he was beaten, his parents sent him to Mandatory Palestine. Later in the war, when Lewy was of fighting age, he voluntarily took up arms against Germany, serving in the Jewish Brigade.

First published in 1964, Lewy's The Catholic Church and Nazi Germany has proven both controversial and influential. Rolf Hochhuth's play The Deputy had appeared only a year earlier, indicting the Vatican for failing to act to save the Jews during the Holocaust; amidst the Vatican's outrage with the play, Lewy's text continued in the same vein, "One is inclined to conclude that the Pope and his advisers—influenced by the long tradition of moderate anti-Semitism so widely accepted in Vatican circles—did not view the plight of the Jews with a real sense of urgency and moral outrage. For this assertion no documentation is possible, but it is a conclusion difficult to avoid."

The text received much praise, including that of Alfred Grosser, who characterized the text as a "terribly precise volume" which demonstrated that "all the documents show the Catholic Church cooperating with the Nazi regime". The Vatican opted to answer the critical allegations by releasing a series of documents aiming to refute the growing perception of the Vatican having been complicit in the Holocaust. One Jesuit priest answering Lewy's text on behalf of the Vatican suggested that Lewy's conclusions were based "not on the record but on a subjective conviction... This ready acceptance of a Nazi-inspired wartime legend is a measure of Lewy's inability to plumb the motives of Pius XII... There is no proof, in this book or anywhere else, that Pius XII thought Nazism was a 'bulwark' in defense of Christianity."

In the context of other historical works examining the legacy of the Vatican in the era of the Holocaust, Lewy's work has been described as "exceedingly harsh".

Lewy had suggested that his America in Vietnam, published in 1978, would "clear away the cobwebs of mythology that inhibit the correct understanding of what went on—and what went wrong—in Vietnam." The text, which argues against traditional or "orthodox" interpretations of the war as an unnecessary, unjust, and/or unwinnable war replete with disastrous mistakes and widespread American atrocities, has proven influential for many western scholars that share similar views of the conflict. It predated and influenced other reinterpretations including those of Norman Podhoretz, Mark Moyar, and Michael Lind. America in Vietnam thus attracted both criticism and support of Lewy for belonging to the "revisionist" school on Vietnam. Lewy argues,

It is the reasoned conclusion of this study... that the sense of guilt created by the Vietnam war in the minds of many Americans is not warranted and that the charges of officially, condoned illegal and grossly immoral conduct are without substance. Indeed, detailed examination of battlefield practices reveals that the loss civilian life in Vietnam was less great than in World War II and Korea and that concern with minimizing the ravages of the war was strong. To measure and compare the devastation and loss of human life caused by different war will be objectionable to those who repudiate or resort to military force as an instrument of foreign policy and may be construed as callousness. Yet as long as wars do take place at all it remains a moral duty to seek to reduce the agony caused by war, and the fulfillment of this obligation should not be disdained. I hope that this book may help demonstrate that moral convictions are not the exclusive possession of persons in conscience opposed to war, and that those who in certain circumstances accept the necessity and ethical justification of armed conflict also do care about human suffering.