Philosopher Martin Heidegger joined the Nazi Party (NSDAP) on May 1, 1933, ten days after being elected Rector of the University of Freiburg. A year later, in April 1934, he resigned the Rectorship and stopped taking part in Nazi Party meetings, but remained a member of the Nazi Party until its dismantling at the end of World War II. The denazification hearings immediately after World War II led to Heidegger's dismissal from Freiburg, banning him from teaching. In 1949, after several years of investigation, the French military finally classified Heidegger as a Mitläufer or "fellow traveller." The teaching ban was lifted in 1951, and Heidegger was granted emeritus status in 1953, but he was never allowed to resume his philosophy chairmanship.

Heidegger's involvement with Nazism, his attitude towards Jews and his near-total silence about the Holocaust in his writing and teaching after 1945 are highly controversial. The Black Notebooks, written between 1931 and 1941, contain several anti-semitic statements, although they also contain several statements where Heidegger appears extremely critical of racial antisemitism. After 1945, Heidegger never published anything about the Holocaust or the extermination camps, and made one sole verbal mention of them, in 1949, whose meaning is disputed among scholars. Heidegger never apologized for anything and is only known to have expressed regret once, privately, when he described his rectorship and the related political engagement as "the greatest stupidity of his life" ("die größte Dummheit seines Lebens").

Whether there is a relation between Heidegger's political affiliation and his philosophy is another matter of controversy. Critics, such as Günther Anders, Jürgen Habermas, Theodor Adorno, Hans Jonas, Maurice Merleau-Ponty, Karl Löwith, Pierre Bourdieu, Maurice Blanchot, Emmanuel Levinas, Luc Ferry, Jacques Ellul, and Alain Renaut assert that Heidegger's affiliation with the Nazi Party revealed flaws inherent in his philosophical conceptions. His supporters, such as Hannah Arendt, Otto Pöggeler, Jan Patočka, Silvio Vietta, Jacques Derrida, Jean Beaufret, Jean-Michel Palmier, Richard Rorty, Marcel Conche, Julian Young, Catherine Malabou, and François Fédier, see his involvement with Nazism as a personal "error" – a word which Arendt placed in quotation marks when referring to Heidegger's Nazi-era politics – that is irrelevant to his philosophy.