There are several psychotherapists who have contributed to existential therapy. In 1946, Victor Frankl wrote "Man's Search for Meaning" after having survived concentration camps during the Holocaust. Frankl introduced the world to logotherapy, the idea that human beings can find meaning in their lives no matter their circumstances. American psychologist Rollo May studied in Europe and brought ideas about existential psychology to the United States in the late 1950s. In 1980, Irvin Yalom named the four "givens" of freedom, isolation, meaninglessness, and death that existential theory is based on.