The Magic Mountain (German: Der Zauberberg, pronounced [deːɐ̯ ˈt͡saʊ̯bɐˌbɛʁk] (listen)) is a novel by Thomas Mann, first published in German in November 1924. It is widely considered to be one of the most influential works of twentieth-century German literature.

Mann started writing The Magic Mountain in 1912. It began as a much shorter narrative that comically revisited the aspects of Death in Venice, a novella that he was preparing for publication. The newer work reflected his experiences and impressions during a period when his wife, who was suffering from a lung complaint, resided at Dr. Friedrich Jessen's Waldsanatorium in Davos, Switzerland for several months. In May and June 1912, Mann visited her and became acquainted with the team of doctors and patients in this cosmopolitan institution. According to Mann, in the afterword that was later included in the English translation of his novel, this stay inspired his opening chapter ("Arrival").

The outbreak of World War I interrupted his work on the book. The savage conflict and its aftermath led the author to undertake a major re-examination of European bourgeois society. He explored the sources of the destructiveness displayed by much of civilised humanity. He was also drawn to speculate about more general questions related to personal attitudes to life, health, illness, sexuality, and mortality. His political stance also changed during this period, from opposing the Weimar Republic to supporting it. Given this, Mann felt compelled to radically revise and expand the pre-war text before completing it in 1924. Der Zauberberg was eventually published in two volumes by S. Fischer Verlag in Berlin.

Mann's vast composition is erudite, subtle, ambitious, but, most of all, ambiguous; since its original publication it has been subject to a variety of critical assessments. For example, the book blends a scrupulous realism with deeper symbolic undertones. Given this complexity, each reader is obliged to interpret the significance of the pattern of events in the narrative, a task made more difficult by the author's irony. Mann was well aware of his book's elusiveness, but offered few clues about approaches to the text. He later compared it to a symphonic work orchestrated with a number of themes. In a playful commentary on the problems of interpretation—"The Making of The Magic Mountain," written 25 years after the novel's original publication—he recommended that those who wished to understand it should read it twice.