Andreas Fritz Hillgruber (18 January 1925 – 8 May 1989) was a conservative German historian who was influential as a military and diplomatic historian who played a leading role in the Historikerstreit of the 1980s. In his controversial book Zweierlei Untergang, he wrote that historians should "identify" with the Wehrmacht fighting on the Eastern Front and asserted that there was no moral difference between Allied policies towards Germany in 1944 and 1945 and the genocide waged against the Jews. The British historian Richard J. Evans wrote that Hillgruber was a great historian whose once-sterling reputation was in ruins as a result of the Historikerstreit.

Hillgruber was born in Angerburg, Germany (present-day Wegorzewo, Poland), near the then East Prussian city of Königsberg (present-day Kaliningrad, Russia). Hillgruber's father lost his job as a teacher under Nazi rule. Hillgruber served in the German Army from 1943 to 1945 and spent the years 1945-48 as a POW in France. During World War II, Hillgruber fought on the Eastern Front, an experience that was later to play a role in his evaluation and writing about the period. In 1945, Hillgruber fled west to escape the Red Army, another experience that was to influence him greatly. After his release, he studied at the University of Göttingen, where he received a PhD in 1952. As a student, Hillgruber was a leading protégé of the medievalist Percy Ernst Schramm, an academic who, as Eberhard Jäckel commented, regarded World War II as a normal war that regrettably, the Nazis were not as skilled at waging as they should have been. Much of Hillgruber's early work reflected Schramm's influence. He spent the decade 1954-64 working as school teacher. In 1960 he married Karin Zieran, with whom he had three children. Hillgruber worked as a professor at the University of Marburg (1965–68), the University of Freiburg (1968–72) and the University of Cologne (1972–89). In the late 1960s he was a target of radical student protesters. He died in Cologne of throat cancer.

In the early 1950s Hillgruber still saw World War II as a conventional war, but by 1965 in his book Hitlers Strategie (Hitler's Strategy), he was arguing that the war was for Hitler a vicious, ideological war in which no mercy was to be given to one's enemies. In his first book, Hitler, König Carol und Marschall Antonescu (Hitler, King Carol and Marshal Antonescu) (1953), a study of relations between Germany and Romania from 1938 to 1944 with a focus on the personalities of Adolf Hitler, King Carol II and Marshal Ion Antonescu, Hillgruber argued for the fundamental normality of German foreign policy, with the foreign policy of the Reich being no different from that of any other power. Because of the importance of Romania's oil without which the Wehrmacht would have been unable to fight after June 1941, Hillgruber paid special attention to the oil question in German-Romanian relations while assigning the "Jewish Question" in Romania to an appendix, which seemed to imply that the plans on part of Marshal Antonescu to murder all of Romania's Jews were of minor importance. By contrast, in his 1965 book Hitlers Strategie, which was Hillgruber's Habilitationsschrift, Hillgruber examined the grand strategic decision-making progress in 1940-41 and concluded that, while Hitler had to adjust to diplomatic, economic, strategic and operational military realities, whenever possible his decisions were influenced by his racist, anti-Semitic and Social Darwinist beliefs. Hillgruber's work on German foreign policy made him one of the leading players in the debates about National Socialist foreign policy.

Hillgruber's writings on the Soviet Union show certain constancies as well as changes over the years. He always argued that the Soviet Union was a brutal, expansionary, totalitarian power, in multiple ways similar to Nazi Germany. But, on the other hand, he argued that Moscow's foreign policy was conducted in a way that was rational and realistic, while the foreign policy of Berlin during the Nazi era was completely irrational and unrealistic. The turning point in Hillgruber's attitude came in 1953-1954 when he was involved in a debate with Gerhard Weinberg and Hans Rothfels on the pages of the Vierteljahrshefte für Zeitgeschichte. Together with Hans-Günther Seraphim, Hillgruber had argued that Operation Barbarossa, the German invasion of the Soviet Union in 1941, had been a "preventive war", forced on Hitler to prevent an imminent Soviet attack on Germany. So effectively did Weinberg and Rothfels demolish Hillgruber's arguments that he repudiated his previous views. Thereafter, he maintained that Operation Barbarossa had been prompted solely by Hitler's ideological belief in the need for Lebensraum (living space) in Russia, where a massive German colonization effort was planned and the entire Russian people were to be reduced to slave status. In the 1970s and 1980s Hillgruber often attacked authors such as David Irving and Viktor Suvorov for putting forward the same arguments as he had done in 1954. Along the same lines, he criticized the American neo-Nazi historian David Hoggan, who argued that the British had provoked World War II in 1939. Hillgruber conceded that there was a "kernel of truth" in Hoggan's claims in that Hitler had believed that he could invade Poland in 1939 without provoking a war with Britain, and was most unpleasantly surprised by the British declaration of war, but maintained that, overall, Hoggan's view of Germany as the victim of an Anglo-Polish conspiracy was simply "preposterous".

The exchange between Hillgruber and Weinberg on the pages of Vierteljahrshefte für Zeitgeschichte in 1953-54 marked the beginning of a long series of clashes between the two historians over interpretations of German foreign policy. In a 1956 book review of Hitler, König Carol und Marschall Antonescu, Weinberg criticized Hillgruber for engaging in what Weinberg considered an apologia for Germany in World War II. Weinberg took issue with Hillgruber's claim that World War II began with the Anglo-French declarations of war on Germany on 3 September 1939 rather with the German attack on Poland on 1 September 1939. In his 1980 monograph The Foreign Policy of Hitler's Germany Starting World War II 1937-1939, Weinberg noted that about the question of the war's origins that "my view is somewhat different" from Hillgruber's. In his 1981 book World in the Balance, Weinberg stated that "Hillgruber's interpretation is not, however, followed here".

Hillgruber's area of expertise was German history from 1871 to 1945, especially its political, diplomatic and military aspects. He argued for understanding this period as one of continuities. In his first address as a professor at Freiburg in 1969, Hillgruber argued for understanding the entire "Bismarck Reich" as one of continuities between 1871 and 1945. For Hillgruber, the continuities of the "Bismarck Reich" were a certain mentalité amongst German elites, namely a Weltanschauung (world view) that emphasized an "either-or" outlook on international relations, Social Darwinism, a deterministic understanding of history, and dreams of worldwide expansionism. However, though Hillgruber paid attention to structural factors, in his opinion it was the actions of individuals that made the difference. As a member of the "Hitler Youth generation" and a World War II veteran, Hillgruber's major interest was why and how Germany failed as a great power. These interests were reflected in the title of one of Hillgruber's better-known books, Die gescheiterte Grossmacht (The Failed Great Power) (1980), in which he examined German power politics from 1871 to 1945. For Hillgruber, there were a number of elements of continuity in German foreign policy in the 1871–1945 period, especially with regard to Eastern Europe. Hans Mommsen wrote that the "ground-laying works of Andreas Hillgruber... suggested the view for the continuities of German policy from the late Wilhelminian period up to the capitulation".

Hillgruber argued that in the 1870s, Germany had won a position of "semi-hegemony" in Europe, and that Otto von Bismarck had three options for preserving that "semi-hegemony":

Hillgruber argued that the "war-in-sight crisis" of 1875 was Bismarck's way of probing the European reaction towards a German "preventive war" to destroy France, and finding that Russia was unsupportive and Britain inclined to intervene, chose the third option. Hillgruber argued that the article under the title "Is War in Sight?" published in a Berlin newspaper close to Bismarck, and which concluded that war was indeed "in sight" was a trial balloon by Bismarck to see what the international reaction would be to a German attack on France. In response to negative international reaction to the "war-in-sight crisis", Bismarck ultimately issued the Bad Kissingen decree of June 25, 1877 in which he called for a situation "in which all powers save France need us and in which they are prevented from forming coalitions against us through their ties to one another". Hillgruber argued that after the "War-in-Sight" crisis that Bismarck followed a conservative foreign policy aimed at upholding the international status quo which was so favourable to Germany.