Viktor Emil Frankl (Austrian German: [ˈfraŋkl̩]; 26 March 1905 – 2 September 1997) was an Austrian neurologist, psychiatrist, philosopher, and Holocaust survivor, who founded logotherapy, a school of psychotherapy that describes a search for a life's meaning as the central human motivational force. Logotherapy is part of existential and humanistic psychology theories.

Logotherapy was promoted as the third school of Viennese Psychotherapy, after those established by Sigmund Freud and Alfred Adler.

Frankl wrote 39 books. The best-selling autobiographical book Man's Search for Meaning is based on his experiences in various Nazi concentration camps.

Frankl was born the middle of three children to Gabriel Frankl, a civil servant in the Ministry of Social Service, and Elsa (née Lion), a Jewish family, in Vienna, in what was then the Austro-Hungarian Empire. His interest in psychology and the role of meaning developed when he began taking night classes on applied psychology while in junior high school. As a teenager, he began a correspondence with Sigmund Freud and Freud asked for permission to publish one of his papers. After graduation from high school in 1923, he studied medicine at the University of Vienna.

In 1924, Frankl's first scientific paper was published in the Internationale Zeitschrift für Psychoanalyse. In the same year, he was president of the Sozialistische Mittelschüler Österreich, the Social Democratic Party of Austria's youth movement for high school students. Frankl's father was a socialist who named him after Viktor Adler, the founder of the party. During this time, Frankl began questioning the Freudian approach to psychoanalysis. He joined Alfred Adler's circle of students and published his second academic paper, "Psychotherapy and Worldview" ("Psychotherapie und Weltanschauung"), in Adler's International Journal of Individual Psychology in 1925. Frankl was expelled from Adler's circle when he insisted that meaning was the central motivational force in human beings. From 1926, he began refining his theory, which he termed logotherapy.

Between 1928 and 1930, while still a medical student, he organized youth counselling centers to address the high number of teen suicides occurring around the time of end-of-the-year report cards. The program was sponsored by the city of Vienna and free of charge to the students. Frankl recruited other psychologists for the center, including Charlotte Bühler, Erwin Wexberg, and Rudolf Dreikurs. In 1931, not a single Viennese student died by suicide.^{[unreliable source?]}

After earning his M.D. in 1930, Frankl gained extensive experience at Steinhof Psychiatric Hospital, where he was responsible for the treatment of suicidal women. In 1937, he began a private practice, but the Nazi annexation of Austria in 1938 limited his opportunity to treat patients. In 1940, he joined Rothschild Hospital, the only hospital in Vienna still admitting Jews, as head of the neurology department. Prior to his deportation to the concentration camps, he helped numerous patients avoid the Nazi euthanasia program that targeted the mentally disabled.

In 1942, just nine months after his marriage, Frankl and his family were sent to the Theresienstadt concentration camp. His father died there of starvation and pneumonia. In 1944, Frankl and his surviving relatives were transported to Auschwitz, where his mother and brother were murdered in the gas chambers. His wife Tilly died later of typhus in Bergen-Belsen. Frankl spent three years in four concentration camps.