A major offshoot of existentialism as a philosophy is existentialist psychology and psychoanalysis, which first
crystallized in the work of Otto Rank, Freud's closest associate for 20 years. Without awareness of the writings of
Rank, Ludwig Binswanger was influenced by Freud, Edmund Husserl, Heidegger, and Sartre. A later figure was
Viktor Frankl, who briefly met Freud and studied with Jung as a young man. His logotherapy can be regarded as
a form of existentialist therapy. The existentialists would also influence social psychology, antipositivist
micro-sociology, symbolic interactionism, and post-structuralism, with the work of thinkers such as Georg Simmel. and Michel Foucault. Foucault was a great reader of Kierkegaard even though he almost never refers this
author, who nonetheless had for him an importance as secret as it was decisive. An early contributor to existentialist psychology in the United States was Rollo May, who was strongly influenced
by Kierkegaard and Otto Rank. One of the most prolific writers on techniques and theory of existentialist psychology
in the USA is Irvin D. Yalom. Yalom states that
Aside from their reaction against Freud's mechanistic, deterministic model of the mind and their assumption of a phenomenological approach in therapy, the existentialist analysts have little in common and have never been regarded as a cohesive ideological school. These thinkers - who include Ludwig Binswanger, Medard Boss, Eugène Minkowski, V.E. Gebsattel, Roland Kuhn, G. Caruso, F.T. Buytendijk, G. Bally and Victor Frankl - were almost entirely unknown to the American psychotherapeutic community until Rollo May's highly influential 1985 book Existence - and especially his introductory essay - introduced their work into this country.
A more recent contributor to the development of a European version of existentialist psychotherapy is the British-based Emmy van Deurzen. Anxiety's importance in existentialism makes it a popular topic in psychotherapy. Therapists often offer existentialist philosophy as an explanation for anxiety. The assertion is that anxiety is manifested of an individual's complete freedom to decide, and complete responsibility for the outcome of such decisions. Psychotherapists using an existentialist approach believe that a patient can harness his anxiety and use it constructively. Instead of suppressing anxiety, patients are advised to use it as grounds for change. By embracing anxiety as inevitable, a person can use it to achieve his full potential in life. Humanistic psychology also had major impetus from existentialist psychology and shares many of the fundamental tenets. Terror management theory, based on the writings of Ernest Becker and Otto Rank, is a developing area of study within the academic study of psychology. It looks at what researchers claim to be the implicit emotional reactions of people confronted with the knowledge that they will eventually die.