The Harden–Eulenburg affair, often simply Eulenburg affair, was the controversy surrounding a series of courts-martial and five civil trials regarding accusations of homosexual conduct, and accompanying libel trials, among prominent members of Kaiser Wilhelm II's cabinet and entourage during 1907–1909.

The affair centred on journalist Maximilian Harden's accusations of homosexual conduct between Philipp, Prince of Eulenburg, and General Kuno, Graf von Moltke. Accusations and counter-accusations quickly multiplied, and the phrase "Liebenberg Round Table" came to be used for the homosexual circle around the Kaiser. The affair received wide publicity and is often considered the biggest domestic scandal of the German Second Empire. It led to one of the first major public discussions of homosexuality in Germany, comparable to the trial of Oscar Wilde in the United Kingdom. The incident which provoked the affair followed on the heels of a public relations gaffe by Wilhelm II. Briefly, in November 1908, Wilhelm II began a vacation at an aristocrat's estate in the Black Forest. One evening after dinner, chief of the Military Secretariat Dietrich von Hülsen-Haeseler was performing a pas seul dressed in a woman's ballet tutu when his heart failed and he died. Ottokar von Czernin, also in attendance, remarked, "In Wilhelm II, I saw a man who, for the first time in his life, with horror-stricken eyes, looked upon the world as it really was." Despite the Emperor's fears, the incident, with its implications of homosexuality at high levels, seemed successfully hushed up.

Hermann Detzner (16 October 1882 – 1 December 1970) was an officer in the German colonial security force (Schutztruppe) in Kamerun (Cameroon) and German New Guinea, as well as a surveyor, an engineer, an adventurer, and a writer. In early 1914, the German government sent Detzner to explore and chart the interior of Kaiser-Wilhelmsland, the imperial protectorate on the island of New Guinea. When World War I broke out in Europe, he was well into the interior and without radio contact. He refused to surrender to Australian troops when they occupied German New Guinea, concealing himself in the jungle with a band of approximately 20 soldiers. For four years, Detzner and his troops provocatively marched through the bush, singing "Watch on the Rhine" and flying the German Imperial flag. He led at least one expedition from the Huon Peninsula to the north coast, and a second by a mountain route, to attempt an escape to the neutral Dutch colony to the west. He explored areas of the New Guinean interior formerly unseen by Europeans and surrendered in full dress uniform, flying the Imperial flag, to Australian forces in January 1919.