Ludwig Binswanger (/ˈbɪnzwæŋɡər/; Swiss Standard German: [ˈbɪnsvaŋər]; 13 April 1881 – 5 February 1966) was a Swiss psychiatrist and pioneer in the field of existential psychology. His parents were Robert Johann Binswanger (1850–1910) and Bertha Hasenclever (1847–1896). Robert's German-Jewish father Ludwig "Elieser" Binswanger (1820–1880) was founder, in 1857, of the Bellevue Sanatorium in Kreuzlingen. Robert's brother Otto Binswanger (1852–1929) was a professor of psychiatry at the University of Jena.

Ludwig Binswanger is the most prominent phenomenological psychologist and the most influential in making the concepts of existential psychology known in Europe and the United States.

In 1907 Binswanger received his medical degree from the University of Zurich. As a young man he worked and studied with some of the greatest psychiatrists of the era, such as Carl Jung, Eugen Bleuler and Sigmund Freud. He visited Freud (who had cited his uncle Otto's work on neurasthenia) in 1907 alongside Jung, approvingly noting his host's "distaste for all formality and etiquette, his personal charm, his simplicity, casual openness and goodness". The two men became lifelong friends, Freud finding Binswanger's 1912 illness "particularly painful", and Binswanger offering Freud a refuge in Switzerland in 1938.

Binswanger became a member of the early 'Freud Group' Jung led in Switzerland; but nevertheless wrestled throughout his life over the place of psychoanalysis in his thinking – his 1921 article on Psychoanalysis and clinical Psychiatry being only one landmark of that lifelong struggle.

Binswanger was also influenced by existential philosophy, particularly after World War I, through the works of Martin Heidegger, Edmund Husserl, and Martin Buber, eventually evolving his own distinctive brand of existential-phenomenological psychology.

From 1911 to 1956, Binswanger was medical director of the sanatorium in Kreuzlingen.

Binswanger is considered the first physician to combine psychotherapy with existential and phenomenological ideas, a concept he expounds in his 1942 book; Grundformen und Erkenntnis menschlichen Daseins (Basic Forms and Knowledge of Human Existence). In this work, he explains existential analysis as an empirical science that involves an anthropological approach to the individual essential character of being human.

Binswanger saw Husserl's concept of lifeworld as a key to understanding the subjective experiences of his patients, considering that "in the mental diseases we face modifications of the fundamental structure and of the structural links of being-in-the-world". For Binswanger, mental illness involved the remaking of a world - including alterations in the lived experience of time, space, body sense and social relationships. Where for example the psychoanalyst might only see "an overly strong 'pre-oedipal' tie to the mother", Binswanger would point out that "such overly strong filial tie is only possible on the premise of a world-design exclusively based on connectedness, cohesiveness, continuity".